Declaration of War got the better of fellow Irish raider Trading Leather to gain revenge on two of England's top colts in the International Stakes at York on Wednesday.

The Group One feature on the opening day of the Ebor Festival was billed as a match between Al Kazeem, who beat Declaration of War in the Eclipse Stakes, and Toronado, who had him in his slipstream in the Sussex Stakes.

But with favourite Al Kazeem seemingly not fully at his best on the fast ground and Toronado failing to shine on his first attempt at the trip, it was left to Aidan O'Brien's 7-1 chance to scoop the STG425,000 ($A746,137) first prize.

Irish Derby winner Trading Leather set out to make it a true stamina test but despite his efforts it was Declaration of War who ran on the stronger to prevail by a length and a quarter.

Al Kazeem came in third in the race won by Frankel 12 months ago, with Toronado coming in last of the six-runner field.

"This lad is tough and hardy," winning jockey Joseph O'Brien said.

"He's been running consistently well and a mile and a quarter (2000m) on hard ground suits him lovely. He travelled very well, relaxed great and toughed it out to the line."

The first two are due to renew rivalry in the Irish Champion Stakes next month while Toronado will revert to his favoured mile trip.

The International result sent a ripple through the pre-post betting for October's Prix de l'Arc de Triomphe, with Al Kazeem pushed out to 10-1 from 6-1, leaving Germany's King George VI and Queen Elizabeth Diamond Stakes winner Novellist heading the market on 4-1.