ASCOT, England (AP) -- So You Think won the Prince of Wales's Stakes at Royal Ascot on Wednesday ahead of Carlton House, the horse owned by Queen Elizabeth II.

It's the 10th Group One victory for the six-year-old So You Think, trained by Aidan O'Brien and ridden by his son, Joseph.

He was narrowly beaten in the same race last year, but finished the 10-furlong trip convincingly this time around.

"My horse relaxed lovely and quickened up very well," jockey O'Brien said.

"I just wanted to get him into a rhythm and get him relaxed, he has loads of class and can quicken and when things work out he's an exceptional horse," O'Brien said. "It's been a great season and I'm very lucky to get to ride some exceptional horses."

The Queen, who is celebrating the Diamond Jubilee to mark her 60-year reign, attended the five-day meet Wednesday.

Carlton House emerged on the far rail to launch a serious challenge, but So You Think saw him off, asserting himself close to home to win by two and a quarter lengths. Godolphin's four-year-old colt, Farhh, finished third, half a length behind Carlton House.

Michael Stoute, trainer of Carlton House, said the Queen's horse gave a good performance and challenged the 4-5 favorite until the finish.

"He couldn't get enough cover as he was a bit off the fence but he was second best, it's as simple as that," Stoute said. "He had every chance but he just found one too good."

The Queen has been to every Ascot meeting since 1945. She's had 20 wins, with the last coming in 2008, when Free Agent won the Chesham Stakes at the 300-year-old race meeting.

This year's meeting had a spectacular start on Tuesday, when Frankel enhanced his status as the world's top-ranked horse on Tuesday, winning the Queen Anne Stakes by 11 lengths to improve to 11-0.

Frankel's trainer said the 4-year-old colt triumphed despite losing a front shoe during the 1-mile race.

"I don't know where it happened but it got loose in the last furlong and came off," Henry Cecil said Tuesday. "But he's fine and lives to fight another day."

Frankel's outstanding performance has put additional pressure on the other undefeated sensation at Ascot, Black Caviar.

The 5-year-old Australian mare is ranked No. 2, behind Frankel, and will aim to extend her record of 21 unbeaten starts when she races in the Diamond Jubilee Stakes on Saturday.

Black Caviar recently broke a long-standing Australian record for consecutive wins, eclipsing the 19 victories of Desert Gold between 1915 and 1917 and of Gloaming from 1919 to 1921.

The 6-furlong Group One race will be Black Caviar's first start outside Australia.

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