Muhaarar came with a late surge under Paul Hanagan to win the July Cup at Newmarket from Tropics by a nose.
The 2-1 favourite, trained by Charlie Hills, was completing a big-race double after victory in the Commonwealth Cup at Royal Ascot last month.
The 2014 runner-up Tropics (25-1) was second again, having led in the six-furlong race before being caught on the line, with Eastern Impact (50-1) third.
Irish challenger Sole Power ran well in fourth over a trip longer than ideal.
Hanagan said he believed throughout the Group One contest that his horse would win, despite coming from behind.
"He didn't really handle the track and the dip and I could only really move on him when he hit the rising ground," he said.
Meanwhile at York, jockey Philip Makin enjoyed a 4,799-1 four-timer, including victory on 25-1 shot Master Carpenter in the John Smith's Cup.
|Racing correspondent Cornelius Lysaght|
|British racing's hunt for a new star sprinter, the first since Muhaarar's dad Oasis Dream, the champion of 2003, may well be over.|
|Though sceptics will frown upon the close proximity of longshots, this was still a fine performance by an improving horse, not least because of the track.|
|Its undulations didn't help the horse's balance - Hanagan said he had "a leg in each county" - and he'll be seen for the remainder of the year on flatter courses like Deauville, Haydock and Ascot when even better can be expected.|