Palace Pier won the St James's Palace Stakes at Ascot 12 months ago in front of empty stands. However, John and Thady Gosden's brilliant miler performed again for a crowd of 12,000 this time.
Racing slightly on the flank in the early stages, Dettori managed to get some cover behind Prince Eiji by halfway.
Entering the final two furlongs, those who took the prohibitive 2/7 price about Palace Pier might have been a little concerned as Dettori got lower in the saddle to ask for his effort.
Although the winning move did not come right away, Palace Pier got into top gear with a furlong to run, with the race over as he took two lengths out of the others.
He was kept on his toes however, as Lope Y Fernandez emerged from the pack to claim second, with Ascot specialist Sir Busker back in third.
Palace Pier's only defeat remains on Champions Day last year at Ascot in the Queen Elizabeth II, when he lost a shoe in heavy ground.
Dettori said: "There wasn't much pace in the race and I had him much further forward than usual.
"I stalked the pace, I had the leaders beat with a furlong and a half to go and then he went a couple of lengths clear and he took it easy with me.
"It was his first time on real good to firm ground, so he wasn't so sure on it - but still, he proved again he's the best miler around. He was in front on his own for a while, so he was taking things easy."
Gosden senior stated: "We suspected a slow pace and we got that slow pace, so the key thing then is don't sit out the back. He did it smoothly, came through and won his race, but he's exactly like his father (Kingman) - as soon as he gets there he thinks he's done enough.
"If I worked him at home with an ordinary horse he'd just stay with him, that's his game.
"When you are odds-on like that there'd be something wrong if you weren't nervous, but it can be a banana skin. Frankie was aware there was no pace so he asserted early, then I noticed he was just hands and heels to keep him going."