Fighting Network RINGS

Yokoi made his professional debut in 2000 and won his first eight fights, mostly fighting in the RINGS organization before moving to compete in PRIDE. After RINGS's demise, he followed fellow judoka Tsuyoshi Kohsaka and joined his Alliance team.

PRIDE Fighting Championships

Yokoi made his debut for the organization on November 24, 2002 at Pride 23 against Dutch kickboxer Jerrel Venetiaan, winning in the third round via armbar submission.

After picking up a TKO win over Wilson Gouveia, the undefeated Yokoi fought former Pride Heavyweight Champion Antônio Rodrigo Nogueira in the opening round of the Pride Total Elimination 2004 tournament. Yokoi performed unexpectedly well,^[1] taking Nogueira down repeatedly with judo throws and pulling out reversals and occasional ground and pound on the Brazilian jiu-jitsu expert, but he ultimately fell to an anaconda choke in the second round for the first loss of his career.

At PRIDE 28, Yokoi faced Heath Herring, but he was soon overwhelmed with a right hook and multiple knees, including illegal strikes to the back to the head that granted Herring a warning. He eventually lost the fight by TKO in the same way. Yokoi looked to make up for his defeat at the next event by taking on Mario Sperry, Brazilian jiu-jitsu world champion and Nogueira's trainer, but after an uneventful round of clinch striking Yokoi was again downed and hit with knees and soccer kicks for the TKO.

Yokoi's final fight in PRIDE was at PRIDE 30, where he faced Quinton "Rampage" Jackson. Yokoi showed himself active again, gaining dominant position with an early omoplata sweep, but Jackson used his superior strength to reverse him and threw heavy punches and kicks until the referee stopped the match.

Post-PRIDE

Yokoi bounced back with a win via rear-naked choke submission win a year after last fight and then fought again a year later in Finland, losing via TKO. With a career record of 11-5, having won only one of his last six fights, Yokoi retired.

Pro Wrestling Zero1 (2002–2007)

Yokoi joined Pro Wrestling Zero1 in May 2002. He started teaming up with other shoot-style wrestlers, namely Wataru Sakata, Yuki Ishikawa and Yoshiaki Fujiwara, and also enjoyed significant wins in the Fire Festival, beating Kohei Sato and Tetsuhiro Kuroda. He spent the rest of the year in random tag team matches, as well as losing efforts to Shinjiro Otani and Kazuhiko Ogasawara. Eventually, he formed a tag team with Kohei Sato in midst of the feud between the native wrestlers and Steve Corino's American faction, and they challenged Corino and CW Anderson for the NWA Intercontinental Tag Team Championship in two separate occasions, though coming short in both.

Around the same time, in which their team was named as Rowdy, they started appearing in All Japan Pro Wrestling as Zero-One representatives. Sato and Yokoi put their eyes in the All Asia Tag Team Championship, taking part in a special league for the vacated title. Rowdy was successful, winning the belts against Turmeric Storm (Kazushi Miyamoto and Tomoaki Honma) in July 2003. They retained the title against challengers like King Adamo and King Joe and Nobukazu Hirai and Shigeo Okumura, but ended up losing it in October to the Zero-One team of Kintaro Kanemura and Tetsuhiro Kuroda.

After the All Japan affair, Yokoi diversified to his singles career aside from Rowdy, and challenged The Predator for the Zero-One United States Heavyweight Championship and Masato Tanaka for the NWA United National Heavyweight Championship. He and Sato also challenged for the NWA tag team titles several times, but they failed. From 2004 to 2006, Yokoi competed sporadically in Hustle as a member of the babyface Hustle Army, teaming up with "Hustle K" Toshiaki Kawada, while trying luck in Zero-One's Fire Festival tournaments and keeping his team with Kohei Sato. He was released from Zero-One in February 2007, leaving pro wrestling altogether.