Housesofparliament gave Aidan O'Brien and Ryan Moore the perfect start to the July meeting when coming out on top in the Bahrain Trophy at Newmarket.
Viewed as a St Leger trial, the winner was given quotes ranging from 10-1 to 14-1 for the final Classic of the season.
Last seen finishing fourth at Royal Ascot in the King Edward VII Stakes behind Across The Stars, the Galileo colt was well on top at the finish.
With two furlongs to travel nearly all of the nine runners still had a chance and were spread right across the track, but the favourite Prize Money was one of the first beaten.
Mick Channon's Harrison briefly looked like stamping his authority on the field but on meeting the rising ground Housesofparliament (9-2) really picked up strongly.
He powered a length and a half clear of Sir Michael Stoute's Platitude, with Harrison third.
Moore said: "Aidan's horses all take their racing very well.
"This horse has run on soft ground all year and it's the first time he's had decent ground and he's relished it.
"He saw it out well and the ground has made a difference to him today."
Kevin Buckley, representing the winning owners, said: "We were quite pleased with that, I suppose it's the best ground he's encountered all year and it's obviously to his liking.
"He saw out the extra furlong well. He settled well in the race, they went slow early on.
"Ryan said he went sooner than he wanted, but the horse responded well.
"Aidan will get him home and we'll see where we go. The trip is not a problem, it's a matter of finding that ground."
Teddy Grimthorpe, racing manager for owner Khalid Abdullah, owner of Platitude, said: "He's run really well and has obviously improved since Ascot.
"At Ascot he was drawn pretty wide and he was wide the whole way round, but the winner (Primitivo) won on merit. He ran a super race and it gave us confidence to come for this.
"I think he stayed well enough to the line. I've not had a real good talk to Frankie (Dettori) yet but we have to be pleased with that.
"He will have some interesting options."
