Juniors

Achieved his top USTA Boys' 18s ranking of No. 1 in 2008. He had a career-high ranking in the International Tennis Federation was No. 14 and he reached the third round of the 2008 Junior Australian Open, Junior Wimbledon Championships, and Junior U.S. Open. He captured both the singles and doubles B18s titles at the 2008 USTA International Spring Championships and 2008 Winter Nationals and the doubles title at Melbourne's Optus Nottinghill ITF Championships. Klahn was a finalist at the 2008 Kalamazoo B18s doubles and the Optus Nottinghill ITF B18s singles. He won the 2006 USTA Nationals (Kalamazoo) B16s doubles and was a member of the Junior Davis Cup squad that competed in Barcelona that same year.^[8]

2008–09

Bradley went to Stanford and was the ITA National Rookie of the Year, Pac-10 Freshman of the Year and an All-Pac-10 First Team selection. Klahn became just the fourth player in school history to claim both the Pac-10 Singles and Doubles Championships in the same year. He led team with an overall record of 35–9, playing mainly at the top two spots of the lineup. He had the team-best 20–5 in dual matches with a 7–1 mark at the No.1 position and 13–4 record at the No. 2 spot. He went 19–8 against nationally ranked opponents and finished with a national ranking of No. 32. He had two different 10-match winning streaks on the year, including a season-best 11-match winning streak from Apr 8 to May 8. His highest-ranked victory was a 6–2, 7–5 win over No. 7 Robert Farah of USC on Apr 25. Klahn claimed the Pac-10 singles title with five consecutive straight-set victories but dropped a hard-fought, three-set decision to teammate Alex Clayton in the final of the ITA Regional Championship. In his first career match, picked up a 6–4, 6–4 win against Kentucky's Brad Cox at the ITA All-American Championships. In double he teamed up with Ryan Thacher for a final No. 28 national ranking and an 11–4 record (7–4 duals). The duo also claimed its first title, winning the Pac-10 doubles crown. advanced to the round of 32 at the ITA All-American Championships and advanced to the doubles semifinals of the ITA Regional Championships with Clayton.^[8]

2009–10

He was an All-American in singles and doubles, All-Pac-10 First Team selection, Pac-10 All-Academic Honorable Mention, Klahn defeated Louisville's Austen Childs 6–1, 6–2 to become NCAA Singles champion, capturing Stanford's 14th collegiate singles title and first since 2000. He almost captured the NCAA Doubles crown as well, advancing to the semifinals. He finished season with a national singles ranking of No. 4. He reached the national title match after knocking off the tournament's top seed and country's No. 2-ranked player in Henrique Cunha of Duke 6–2, 6–2. He notched two different season-best nine-match winning streaks and led team in victories with a 41–8 overall record while also going 17–5 in duals and playing all his matches at the No. 1 position. Klahn was 23–8 against nationally ranked opponents, 15–6 against Pac-10 foes, 12–2 in home matches and 7–4 in three-set matches. He posted a 3–2 mark against players ranked in the top-10 at the time of the match. Klahn opened the year by winning 18 of his first 20 matches. He partnered exclusively with Ryan Thacher in doubles and the duo finished 40–8 overall, 17–3 in duals, 14–5 against Pac-10 opponents, 13–6 against nationally ranked foes and 11–0 in home matches. The dominant pairing claimed two doubles titles on the year, taking home the hardware at the ITA Northwest Regional Championships and ITA National Indoor Championships.^[8]

2010–11

He was again an All-American in singles and doubles, All-Pac-10 First Team honoree and Pac-10 All-Academic Honorable Mention selection. he advanced to quarterfinals of NCAA Singles Championship and earned a final national singles ranking of No. 6. He also led team with a 36–11 overall record. He was 24–9 against nationally ranked opponents with his highest-ranked victory was a 6–4, 6–2 rout of No. 5 Michael Shabaz from Virginia in the NCAA Tournament team portion. He reached the semifinals of the D'Novo/ITA All-American Championships and captured the singles title at the Sherwood Cup, repeating as the tourney champion. He finished runner-up finish at the Pac-10 Championships. In doubles again he partnered exclusively with Ryan Thacher for team-best records overall (43–8) and in duals (19–3), while finishing 16–7 against nationally ranked foes. Klahn and Thacher earned a final national doubles ranking of No. 4. They were named Pac-10 Doubles Team of the Year and were runner-up finish at NCAA Doubles Championships. They were the first Stanford doubles team to reach NCAA Doubles Championships final since 2004. He pocketed three tournament doubles titles during the year (Pacific Coast Doubles, Sherwood Cup and ITA National Indoor Championships consolation).^[8]

2011–12

Klahn at the 2018 Wimbledon Championships

He was an ITA Scholar Athlete and All-American in both singles and doubles. As well as an All-Pac-12 First Team selection, Pac-12 All-Academic Honorable Mention selection and reached semifinals of the NCAA Singles Championship. He went 18–6 overall in singles and 14–5 in duals. He played mainly at the No. 1 spot He earned a final No. 12 in the national singles ranking and was 11–6 against nationally ranked opponents, 4–1 in tournament matches and 6–1 against conference The highest-ranked opponent he defeated was No. 3 Eric Quigley of Kentucky, prevailing 6–1, 6–2 in the NCAA Championships round of 16. He went 8–2 over his final 10 matches of the year in singles and in doubles with Ryan Thacher, compiled a 19–3 record overall and was 11–2 in duals. The duo earned a final No. 9 national ranking and advanced to quarterfinals of the NCAA Doubles Championships. Klahn and Thacher won the Pacific Coast Doubles crown in March, defending last year's title and earning seventh career doubles championship. They were the first tandem to capture back-to-back titles at the historic tournament since former Stanford standouts Jared Palmer and Jonathan Stark accomplished the feat in 1990–91.^[8]

2013: Top 100 debut

The American finished in Top 100 for 1st time in his career after posting a 40–17 record in Challengers and winning 2 titles in 5 finals. Also 11–2 in Futures with 1 title. He was the youngest of 6 Americans in year-end Top 100. He won 1st Challenger title at Aptos (d. Evans) in August and won 2nd at Yeongwol, South Korea (d. Daniel) in November. Klahn also reached back-to-back finals at Winnetka (l. to Sock) and Binghamton (l. to Kuznetsov) in July, and reached final at Traralgon, Australia (l. to Bhambri) in October...He then reached back-to-back Futures finals in March, winning 1st career Futures title at U.S.A. #8 (d. Cho) and the week before at U.S.A. #7 (l. to Singh).

In Grand Slam play Klan went 1–1, reached 2R at US Open for 2nd year in a row (l. to Lopez), fell in qualifying at Australian Open (l. to Berankis in Q2), Roland Garros (l. to Velotti in Q1) and Wimbledon (l. to Peliwo in Q1) He compiled records of 1–2 on hard, 0–1 on clay and earned a career-high $153,368.^[6]

2022–2023: Comeback from surgery, retirement

He came back in 2022 after a year and a half absence following a back surgery in December 2020.^[9] His first tournament in singles was at the 2022 French Open qualifying where he used his protected ranking. His first tournament back in doubles was the 2022 San Diego Open in September where he participated in singles in qualifying using a protected ranking and in doubles as a wildcard reaching the semifinals with Fernando Verdasco.

In August 2023, Klahn made his final professional appearance at the 2023 Golden Gate Open.^[10]

Singles: 18 (9–9)

Result	W–L	Date	Tournament	Tier	Surface	Opponent	Score
Loss	0–1	Sep 2009	USA F22, Claremont	Futures	Hard	Matt Bocko	6–7(4–7), 3–6
Loss	0–2	Mar 2013	USA F7, Calabasas	Futures	Hard	Sanam Singh	3–6, 6–1, 6–7(3–7)
Win	1–2	Mar 2013	USA F8, Costa Mesa	Futures	Hard	Cho Min-hyeok	6–3, 6–3
Loss	1–3	Jul 2013	Winnetka, US	Challenger	Hard	Jack Sock	4–6, 2–6
Loss	1–4	Jul 2013	Binghamton, US	Challenger	Hard	Alex Kuznetsov	4–6, 6–3, 3–6
Win	2–4	Aug 2013	Aptos, US	Challenger	Hard	Dan Evans	3–6, 7–6(7–5), 6–4
Loss	2–5	Nov 2013	Traralgon, Australia	Challenger	Hard	Yuki Bhambri	7–6(15–13), 3–6, 4–6
Win	3–5	Nov 2013	Yeongwol, South Korea	Challenger	Hard	Taro Daniel	7–6(7–5), 6–2
Win	4–5	Jan 2014	Maui, US	Challenger	Hard	Yang Tsung-hua	6–2, 6–3
Win	5–5	Feb 2014	West Lakes, Australia	Challenger	Hard	Tatsuma Ito	6–3, 7–6(11–9)
Win	6–5	Nov 2014	Traralgon, Australia	Challenger	Hard	Jarmere Jenkins	7–6(7–5), 6–1
Loss	6–6	Mar 2017	USA F11, Calabasas	Futures	Hard	Sebastian Fanselow	3–6, 2–6
Loss	6–7	Oct 2017	Monterrey, Mexico	Challenger	Hard	Maximilian Marterer	6–7(3–7), 6–7(6–8)
Loss	6–8	Oct 2017	Fairfield, US	Challenger	Hard	Mackenzie McDonald	4–6, 2–6
Loss	6–9	Jan 2018	Newport Beach, US	Challenger	Hard	Taylor Fritz	6–3, 5–7, 0–6
Win	7–9	Jul 2018	Gatineau, Canada	Challenger	Hard	Ugo Humbert	6–3, 7–6(7–5)
Win	8–9	Nov 2018	Houston, US	Challenger	Hard	Roy Smith	7–6(7–4), 7–6(7–4)
Win	9–9	Jul 2019	Winnetka, US	Challenger	Hard	Jason Kubler	6–2, 7–5

Doubles: 19 (10–9)

Result	W–L	Date	Tournament	Tier	Surface	Partner	Opponents	Score
Loss	0–1	Apr 2013	Sarasota, US	Challenger	Clay	Steve Johnson	Ilija Bozoljac Somdev Devvarman	7–6(7–5), 6–7(3–7), [9–11]
Win	1–1	Jun 2013	Romania F3, Bacău	Futures	Clay	Michael Venus	Piotr Gadomski Tristan Lamasine	7–6(7–4), 6–7(4–7), [14–12]
Win	2–1	Jul 2013	Binghamton, US	Challenger	Hard	Michael Venus	Adam Feeney John-Patrick Smith	6–3, 6–4
Loss	2–2	Jul 2013	Lexington, US	Challenger	Hard	Michael Venus	Frank Dancevic Peter Polansky	5–7, 3–6
Loss	2–3	Oct 2013	Tiburon, US	Challenger	Hard	Rajeev Ram	Austin Krajicek Rhyne Williams	4–6, 1–6
Win	3–3	Nov 2013	Yokohama, Japan	Challenger	Hard	Michael Venus	Sanchai Ratiwatana Sonchat Ratiwatana	7–5, 6–1
Loss	3–4	Sep 2014	Napa, US	Challenger	Hard	Tim Smyczek	Peter Polansky Adil Shamasdin	6–7(0–7), 1–6
Win	4–4	Oct 2014	Tiburon, US	Challenger	Hard	Adil Shamasdin	Carsten Ball Matt Reid	7–5, 6–2
Win	5–4	Nov 2014	Yokohama, Japan (2)	Challenger	Hard	Matt Reid	Marcus Daniell Artem Sitak	4–6, 6–4, [10–7]
Loss	5–5	Jan 2015	Nouméa, New Caledonia	Challenger	Hard	Jarmere Jenkins	Austin Krajicek Tennys Sandgren	6–7(2–7), 7–6(7–5), [5–10]
Loss	5–6	Jan 2017	Maui, US	Challenger	Hard	Tennys Sandgren	Austin Krajicek Jackson Withrow	4–6, 3–6
Win	6–6	Mar 2017	USA F11, Calabasas	Futures	Hard	Connor Smith	Farris Fathi Gosea Alex Lawson	6–4, 6–7(5–7), [10–5]
Loss	6–7	Jul 2017	Winnetka, US	Challenger	Hard	Kevin King	Sanchai Ratiwatana Christopher Rungkat	6–7(4–7), 2–6
Win	7–7	Jul 2017	Gatineau, Canada	Challenger	Hard	Jackson Withrow	Hans Hach Verdugo Vincent Millot	6–2, 6–3
Loss	7–8	Sep 2017	Shanghai, China	Challenger	Hard	Peter Polansky	Toshihide Matsui Yi Chu-huan	7–6(7–1), 4–6, [5–10]
Win	8–8	May 2018	Bordeaux, France	Challenger	Clay	Peter Polansky	Guillermo Durán Máximo González	6–3, 3–6, [10–7]
Win	9–8	Jul 2018	Gatineau, Canada	Challenger	Hard	Robert Galloway	Darian King Peter Polansky	7–6(7–4), 4–6, [10–8]
Win	10-8	Jul 2019	Winnetka, US	Challenger	Hard	JC Aragone	Christopher Eubanks Thai-Son Kwiatkowski	7-5, 6-4
Loss	10-9	Nov 2019	Knoxville, USA	Challenger	Hard (i)	Sem Verbeek	Hans Hach Verdugo Adrián Menéndez Maceiras	6–7(6–8), 6–4, [5–10]

Singles

Doubles