The 8-1 shot, ridden by Andrea Atzeni, charged powerfully down the far side of the track to win by a length.
"He travelled brilliantly throughout the race and picked up when he got daylight," said Atzeni.
Strong-travelling mare Euro Charline (12-1), with Ryan Moore on board, finished second ahead of Endless Drama (8-1) and 3-1 favourite Limato.
"Belardo is a good horse on his day and it's a pleasure to be back on him," added Atzeni, who was riding the Roger Varian-trained four-year-old for the first time since October 2014.
"I remember when I first sat on him as a two-year-old I told Roger he was the fastest I'd sat on.
"It's just on the easy side of good and probably at his very best he just needs a bit of cut."
The Godolphin-owned Belardo came late to claim a Group One success in the Al Shaqab Lockinge Stakes at Newbury.