Mark Johnston's Royal Ascot winner Hartnell followed up his win in the Queen's Vase with an all-the-way success in the Bahrain Trophy at Newmarket.
Stepping back in trip, Joe Fanning was able to dictate his own pace at the head of affairs and never really looked like being hauled back.
Sent off at 9/4, his main market rivals were John Gosden's Forever Now and Richard Hannon's Windshear but the latter was one of the first in trouble before running on again to claim second.
Hartnell was clipped to 12/1 from 14/1 by Sky Bet for the Ladbrokes St Leger and Michael Shinners, representing the Leeds-based firm, said: "He was impressive enough but he got the run of the race and we're happy to lay him at present."
Fanning said: "He's won well today, he kept straight and at the two-pole I thought it would take a good one to get by me. He quickened up well.
"He gave me a better feel today than at Ascot. There was a bit more juice in the ground - when he ran last year in France it was heavy ground."
Johnston said: "Joe said he gave him a much better feel there than he did at Ascot. He wonders a little bit now whether the two miles there was stretching him a little bit.
"He burst clear so comfortably at Ascot and said today that two down he couldn't see anything getting past him. He had plenty left in the tank, he never flicked his stick at all and the horse went as straight as a gun barrel.
"That's the horse we thought we had. We were very bullish in the spring when he seemed to be going better than Somewhat (who was placed in the Coral-Eclipse). Then both of them did not really live up to expectations in their first couple of runs, but that's him coming good now.
"The St Leger has got to be the target. We were thinking of that even at the beginning of the year.
"What we do between now and then, we'll have to go home and have a think about.
"Ground may be an issue as he has run his best races with some cut in the ground, so maybe it was a bit too fast for him at Lingfield and at Ascot perhaps. The Leger has to be the number one target.
"I've thought since last year that this was a really classy horse, but lots of classy horses win the Queen's Vase. I'm not going to belittle the Queen's Vase."
Hannon is also thinking of Doncaster for the runner-up.
He said: "He ran a good race and stays the trip well, but I think the race at Ascot (second to Elite Army in the King George V Stakes) left its mark a bit. He'll have a break now. We can still look at the Leger later on, there's no reason why not."
Third was Forever Now, and Gosden said: "He didn't like the ground, which has come loose on top.
"It has probably done his handicap mark no good but he has run a lovely race as this was a good edition of it and the first two horses are smart horses."