Big Orange has led all the way under James Doyle to win the Gold Cup at Royal Ascot for trainer Michael Bell, holding off a late challenge from last year's winner, the Lloyd Williams-owned Order Of St George.

Doyle was positive from the start, disputing the early lead with Quest For More before opting to do it the hard way and go on his own over the gruelling 4000 metres.

Ryan Moore put Order Of St George to sleep at the back of the field, giving Big Orange a healthy head start.

Big Orange was still in control in the home straight with Moore presenting Order Of St George late.

It looked as though Big Orange would be swallowed up, but he kept finding under pressure and was on top by a short head at the line.

Big Orange, who has run in two Melbourne Cups, firmed from $41 to $26 for this year's race but is now likely to get too much weight.

Doyle, who gained the ride because Frankie Dettori was injured, paid tribute to Big Orange's spirit.

"Blimey, he's as tough as they get!" Doyle said.

"It was great to get the call-up. Unfortunately Frankie couldn't have got the injury at a worse time.

"Frankie's a real star. He called me a couple of nights ago and I was probably on the phone for about 20 minutes getting instructions and him telling me all about the horse. He was spot-on.

"Frankie said to me 'whatever you do, don't interfere with him'. He knows what speed he wants to go at and you just sit as a passenger.

"I had Frankie's voice in my head as I just eased him out and let him go to the front and the rest was history."

The first two were six lengths in front of Harbour Law.