[9] After a break of two months, Grey Momus reappeared in the Hopeful Stakes at Newmarket on 3 October for which he started 4/7 favourite despite carrying top weight.

[12] At the Newmarket Houghton meeting on 30 October, Grey Momus was pitted against Colonel Peel's four-year-old filly Vulture, over five furlongs in a match which was highly anticipated.

[15] By the end of December, Grey Momus, after his mixed results at Newmarket, was third favourite for the Derby behind D'Egville and a son of Cobweb who was later named Phoenix.

The grey colt was sent into the lead by John Day from the start and was never headed, winning easily[17] by a length won from Saintfoin, with the favourite, Bamboo in third place.

[18] The supporters of the beaten favourite were dissatisfied by their horse's defeat and as a result, Grey Momus and Bamboo ran a match race at level weights over the same course and distance three days later.

Grey Momus increased his superiority over his rival to win a prize of 300 sovereigns very easily by two lengths after Bamboo had led for the first half of the race.

[22] Two weeks after his defeat in the Derby, Grey Momus was sent to Ascot where he ran against older horses in the Gold Cup over a distance of two and a half miles.

On the opening day of the First October meeting he contested the Grand Duke Michael Stakes over ten furlongs and won at odds of 1/4 from Dash, with the 1000 Guineas winner Barcarolle in third.

[27] On his final start of the year, Grey Momus ran a £500 match at Newmarket's Houghton meeting on 2 November, and was beaten over two miles by Caravan.

[28] This defeat confirmed the belief of some observers that the successes of Grey Momus in 1838 owed more to his connections clever selection of targets rather than any exceptional ability.

The previously undefeated Yorkshire colt was strongly favoured in the betting, but Grey Momus won the two mile contest "in a canter" by two lengths.