Following an 86-day break, Mozart was stepped up in class in the £400000 Tattersalls Houghton Sales Stakes, again over 7 furlongs, on the Rowley Mile Course at Newmarket in September. Despite facing 25 rivals, he again started favourite, at 11/10, and, although his task was made easier by the second favourite, Eminence, refusing to race, Mozart took the overall lead inside the final furlong and held on well, under Mick Kinane, to win by a length. The following month, Mozart was stepped up in class again in the Dewhurst Stakes over the same course and distance but, having held every chance with two furlongs to run, weakened in the final hundred yards to finish fourth, beaten 2 lengths, behind comfortable winner Tobougg.
Mozart reappeared in the 2,000 Guineas Trial Stakes, over a mile, at Leopardstown in April, 2001, but finished only third of five, beaten 3¼ lengths, at odds of 1/4. He was again beaten, albeit narrowly, at odds-on in the Tetrarch Stakes, back over 7 furlongs, at the Curragh the following month, before taking his chance in the Irish 2,000 Guineas, over a mile, at the Co. Kildare track three weeks later. Despite carrying the third colours of owner Michael Tabor, Mozart belied odds of 20/1 by finishing second, although he was easily brushed aside by his equally unfancied stable companion, Black Minnaloushe, in the closing stages.
Consequently, Mozart started favourite, at 7/4, for the Jersey Stakes, back over 7 furlongs, at Royal Ascot. Reunited with Mick Kinane, he made most of the running and, despite being hard ridden, held on well close home to beat the strong-finishing Alderbaran by a neck and record his first success at Pattern level.
However, it was on his next start, when tried over 6 furlongs for the first time, and pitted against specialist sprinters at the highest level, in the July Cup at Newmarket that Mozart proved something of a revelation. Sent off favourite again, at 4/1, he made all on the stands’ side and was ridden clear in the final furlong to beat King’s Stand Stakes winner Cassandra Go decisively, by 3½ lengths, with Sprint Stakes winner Misraah a further length behind in third place. On-course going officially described as ‘good’, the winning time, of 69.86 seconds, was only three-tenths of a second slower than the record set by Stravinsky, also trained by O’Brien and ridden by Kinane, two years earlier.
After such a devastating demonstration of speed, O’Brien had no qualms about letting Mozart take his chance in the Nunthorpe Stakes, over 5 furlongs, at York the following month. In fact, shortly after the July Cup he simply said, ‘If we run in that [the Nunthorpe Stakes] we would have to let him go a bit earlier, that’s all.’ It appears that the betting public took the Master of Ballydoyle at his work because, on the Knavesmire, Mozart started 4/9 favourite and never gave his supporters an anxious moment, taking the lead just after halfway and running on strongly to beat subsequent Haydock Sprint Cup winner Nuclear Debate by 2 lengths.
Sent to Belmont Park in Elmont, New York for the Breeders’ Cup Sprint, back over 6 furlongs, in October, Mozart missed the break and was never involved, eventually finishing eleventh of 14, beaten 10 lengths, behind Squirtle Squirt. Nevertheless, his two domestic Group One victories resulted in Mozart being named Cartier Champion Sprinter of 2001.