After leaving Epsom wondering what might have been on Oaks day, it was back to business as usual for Aidan O'Brien as Anthony Van Dyck gave the trainer a record-equalling seventh victory in the Derby.

Having seen his dreams of completing a clean sweep of British Classics this season ended following the narrow defeat of Pink Dogwood in the Oaks on Friday (Saturday AEST), the champion Irish trainer came out on top a day later in the race he values above all else on the calendar.

Victory for the 13-2 chance, one of seven runners for O'Brien, looked unlikely at one stage, with Seamie Heffernan on and off the bridle, but he warmed to the task to get up on the rail to defeat the gallant Madhmoon by half a length.

"We never thought we would be in the position we are in now and that is why we kind of have to pinch ourselves every day - that we are working with the best people and with the most incredible horses with unbelievable pedigrees and physiques and in an incredibly facility," O'Brien said.

"All the big races, we train the horses for them and we do our best. Sometimes there is a lot of stuff you can't control and sometimes the ducks just fall right for you in a row and it happens."

The win was a first from 12 attempts for Heffernan who is a a part of the large team at the trainer's Irish base at Ballydoyle.

"Seamus is an unbelievable fellow. He is a world-class jockey and always has been," O'Brien said.

"I can't tell you how delighted we are for him. Day in, day out he puts it all in and is incredibly experienced. As a horseman and jockey, he is second to none."

The win was one to savour for 46-year-old Heffernan.

"I've been around plenty of Derby winners," he said.

"I rode his father (Galileo) in his trial and won it. It means a lot to win it.

"I'm always confident riding for Aidan, as anything can happen. It doesn't matter whether they are favourite or a big price, as he trains them all for the big day.

"There is no other yard in Ireland where I would have got the chance to go round in the Derby 12 times.

"It was only a matter of time. I wasn't going to give up until I at least won one. The Derby is the top race. It is the best, maybe then the Arc, then the Breeders' Cup."