1976: two-year-old season

J.O. Tobin began his racing career with a win over Chain of Reasoning in the Fulbourn Maiden Stakes over six furlongs at Newmarket Racecourse on 8 July.^[3] Three weeks later, the colt was moved up in class for the Group Two Richmond Stakes at Goodwood Racecourse. Ridden by Lester Piggott, he started the 8/11 favourite^[4] and won from Priors Walk and Tachypous, a colt who later won the Middle Park Stakes.^[5]

J.O. Tobin's next race was the Champagne Stakes at Doncaster Racecourse in September, for which he was made the 4/9 favourite. In what was described by Timeform as a "breathtaking" performance, Piggott sat motionless on the colt until the final furlong, at which point J.O. Tobin accelerated clear of his rivals to win by four lengths from the filly Durtal. The form of the race was subsequently boosted when Durtal won the Cheveley Park Stakes and was rated the best two-year-old filly of the year in Britain. On his final appearance of the season, J.O. Tobin was matched against the outstanding French two-year-old Blushing Groom in a highly anticipated race for the Grand Critérium over 1600 metres at Longchamp Racecourse on 10 October. Blushing Groom, ridden by Henri Samani, started 4/5 favourite after wins in the Prix Robert Papin, Prix Morny and Prix de la Salamandre whilst J.O. Tobin, ridden as usual by Piggott, started at odds of 5/4. Piggott tracked Samani, but when Blushing Groom took the lead in the straight, J.O. Tobin was unable to maintain his challenge and finished third, beaten four lengths and a head by Blushing Groom and Amyntor.^[5]

1977: three-year-old season

When Murless retired at the end of the 1976 season, Pope brought the horse back to the United States, where he was trained by former jockey and U.S. Racing Hall of Fame inductee John H. Adams. For his new trainer, the colt won the Coronado Handicap at Hollywood Park Racetrack in April and then finished fifth behind Seattle Slew in the Preakness Stakes. By the time J.O. Tobin met Seattle Slew in the Swaps Stakes, the latter had completed the Triple Crown in the Belmont Stakes to take his winning sequence to nine. J.O. Tobin led from the start and quickly went clear of Seattle Slew and Text. On the final turn, Seattle Slew began to weaken, and J.O. Tobin steadily increased his advantage in the straight. He beat Affiliate by 83⁄4-lengths in a time of 1:583⁄5 missing the track and world record for 11⁄4 miles by two-fifths of a second. Seattle Slew finished 4th, 16 lengths behind. Ridden by Bill Shoemaker, J.O. Tobin led from start to finish, running very fast fractions of 222⁄5 to the 1/4 mile, 452⁄5 to the 1/2 mile, 1:091⁄5 to the 3/4 mile & 1:333⁄5 to the mile.^[6]

1978: four-year-old season

In 1978, J. O. Tobin's race conditioning was taken over by future Hall of Fame trainer Laz Barrera, who guided him to wins in six Graded stakes races and American Champion Sprint Horse honors. On his first appearance of the season, he won the Malibu Stakes by five and a half lengths at Santa Anita Park in January.^[7] He went on to win the Californian Stakes, Tom Fool Handicap, Los Angeles Handicap, San Bernardino Handicap, and Premiere Handicap. He was voted American Champion Sprint Horse at the Eclipse Awards for 1978.