Dayjur made his first racecourse appearance in the six furlong Kennett Maiden Stakes at Newbury on 15 June. He started the 8/15 favourite against thirteen opponents and won "easily" by a length. A month later he was moved up in class for the Listed Manton Rose Bowl Stakes over the same course and distance. He started 8/13 favourite but was beaten half a length by the Clive Brittain-trained Rushmore. At the end of the year he was given a "Hobday" operation to improve his breathing.
1990: three-year-old season
Spring
In the spring of 1990, Dayjur was aimed at the 2000 Guineas, but ran disappointing in his trial race, finishing seventh of the ten runners in the European Free Handicap over seven furlongs at Newmarket. He was moved back down to six furlongs and won a minor race at Nottingham before being beaten a head by Tod in a similar event at Newbury. Ten days after his disappointing run at Newbury, Dayjur contested his first Group Race when he was pitted against more experienced sprinters in the five furlong Temple Stakes at Sandown Park Racecourse. On this occasion, Carson allowed the colt to lead from the start and he won by two lengths without being seriously challenged.
Summer
In June, Dayjur was sent to Royal Ascot for the five furlong King's Stand Stakes, which was then a Group Two race. Hern was concerned about the soft ground, but Hamdan Al Maktoum insisted on running him. Dayjur led almost from the start and drew clear in the final two furlongs to beat the French colt Ron's Victory by two and a half lengths, with a gap of six lengths to the rest of the field. In September, Ron's Victory won the Diadem Stakes by ten lengths. In August, Dayjur was made 8/11 favourite for the Group One Nunthorpe Stakes at York, with the King George Stakes winner Argentum the only horse seriously supported against him. Once again, Carson allowed him to lead from the start and Dayjur pulled away in the closing stages to win by four lengths in a course record time of 56.16. The Racing Post described the performance as "very impressive".
Autumn
In September, Dayjur was moved back up to six furlongs for the Ladbroke Sprint Cup at Haydock Park. He started the 1/2 favourite against a field which included the July Cup winner Royal Academy and the Prix Maurice de Gheest winner Dead Certain. Dayjur led from the start, went clear inside the final quarter mile and held the late challenge of Royal Academy to win by one and a half lengths. In October, Royal Academy won the Breeders' Cup Mile. On his final European start, Dayjur contested the Prix de l'Abbaye at Longchamp Racecourse in Paris. Only five horses appeared to oppose him and he led from the start before winning by two lengths. He was eased down in the closing stages and lost some ground when appearing to jump a shadow cast across the course. During his final race, the 1990 Breeders' Cup Sprint at Belmont Park, Dayjur overcame a difficult wide draw and after bitterly contesting the lead with Safely Kept, had got on top and looked set for a famous victory. However, in the closing seconds of the race, Dayjur jumped a dark shadow cast over the track - and another at the line - allowing the filly to claim victory by a neck.
He retired to the Shadwell Racing farm in Kentucky of his owner Sheikh Hamdan Al-Maktoum, from where he has sired several good winners like Tipsy Creek, Hayil and Millstream. On January 18, 2010 it was announced that Dayjur had been retired from stud duty. On 25 September 2013 Dayjur was euthanized Shadwell "due to the infirmities of old age".
