Frankie Dettori has powered home on Golden Horn to win the Epsom Derby and crown his return to the big time after his well-documented drugs ban and split with Godolphin.

It was a second Derby win for both Dettori who won on Authorized in 2007 and also for John Gosden who trained Benny The Dip to win in 1997.

Golden Horn came from the back in Saturday's showpiece to beat his stablemate Jack Hobbs, ridden by William Buick, by 3-1/2 lengths.

With a question mark over his mount's stamina 44-year-old Dettori held Golden Horn up as long as possible.

Buick got to work on Jack Hobbs and they briefly took command but Dettori was cruising up the outside, and once in front stayed on stoutly to land the famous spoils.

Basking in his resurgence after after falling out with Sheikh Mohammed's Godolphin and a six month-ban for cocaine use, Dettori said Golden Horn had lived up to his 13-8 favouritism.

"The horse was magnificent. He did win it by a long way in the end he flew at the end," Dettori said.

"He hit a flat spot and I thought I can't get him going but then he flew.

"In the last 100 yards I couldn't believe I had won the Derby again. I have to pinch myself.

"I can't get to the bottom of this horse and I couldn't pull him up at the end of the race. He is an unbeaten Derby winner. What more can you say?!"

Gosden, who talked owner-breeder Anthony Oppenheimer into paying the Derby late entry fee, praised Dettori's ride.

"I thought Frankie dropped him out beautifully. He rode a cool race," he said.

"Jack Hobbs has run a blinder and all being well he can go to Ireland for the Derby."

Oppenheimer had never regarded his colt as a Derby candidate because of doubts about the mile-and-a-half (2400m) and had to pay STG 75,000 ($A150,000) - money well spent as Golden Horn is now worth tens of millions as a stallion.

"Such a thrill - amazing, I can hardly believe it amazing," Oppenheimer said.

In an intriguing twist, Dettori had ridden Jack Hobbs to second in the Dante Stakes, with William Buick on the winner Golden Horn.

But after Dettori's former employers Godolphin had bought a controlling stake in Jack Hobbs and so claimed Buick, their new retained rider, it left the way clear for Dettori to ride Golden Horn.