Qualify has caused a major upset in the Oaks at Epsom, giving trainer Aidan O'Brien his fifth win in the Classic.

The filly came with a late run under Colm O'Donoghue on Friday to foil well-supported favourite and 1000 Guineas winner Legatissimo.

As expected, Star Of Seville set the early pace under William Buick, closely tracked by the eventual winner's stablemate, Together Forever.

Turning for home Qualify only had three behind her as the race began to reach the business end.

Despite having a wall of horses in front of him, O'Donoghue knew exactly what he had up his sleeve aboard the rank outsider and the 50-1 chance made a late surge to win by a short head.

Owned by John Murrell, Qualify is one of the few horses O'Brien trains outside the Coolmore operation.

"We always thought she was a very good filly," O'Brien said.

"It just took a couple of runs to learn how to ride her as a two-year-old. Joseph (O'Brien) said he was going to ride her stone cold in a Group race at the Curragh one day and she bolted in.

"We knew up to a mile-and-a-quarter (2000m) she would be a top-class filly, but we weren't sure about a mile and a half. Colm gave her a peach of a ride today to produce her on the line. It was class."

For winning jockey O'Donoghue the victory represented his first Classic success in England, and one that he placed near the top of his achievements in the saddle.

"I'm not surprised, she's always shown a lot of pace and is a well-balanced filly," he said.

"This is obviously a highlight in my career. I've been fortunate to ride around the world and have some big winners, but an Oaks is very special."