The highly-anticipated debut of Hydrogen has not brought the win his owner had hoped with the colt sixth at Newmarket.

Had the son of Galileo not been the most expensive yearling sold at auction in 2012 at 2.5 million guineas ($A3.9 million) his effort would have registered as just about reasonable.

The winner of the Maiden Stakes, Wonderstruck, boasts virtually as impressive a pedigree as he does, being a half-sister to the top-class Grandera and George Washington.

But the Royal Ascot-bound filly went rather unnoticed with most eyes trained on Hydrogen.

Hydrogen (4-1) is in the care of Peter Chapple-Hyam, who saddled his half-brother Authorized to win the 2007 Derby.

He was starting off over a mile-and-a-half (2400m) on the July Course after suffering a series of hold-ups as a two-year-old and beyond.

Jamie Spencer dropped him out at the rear of the field, and Hydrogen briefly flickered into life a couple of furlongs (400m) from home before his effort petered out.

Wonderstruck (11-4), a daughter of Sea The Stars, was Frankie Dettori's only ride on the card and built upon the promise she showed at Ascot three weeks earlier when third to the likely Oaks runner Marsh Daisy.

"Obviously we would have loved him to have won, but it's all part of his education and he just got very tired at the end," David Redvers, racing manager for Qatar Racing, said of Hydrogen: .

"He quickened well with the first smack, quickened again with the second smack and followed Frankie through, then got tired.

"I think all he does is gallop and in time he might step up to a mile and six furlongs (2800m) and turn into a Cup-type horse if he proves good enough."