Aidan O'Brien secured his 200th victory at the highest level as Was ran out a surprise 20-1 winner of a rough renewal of the Investec Oaks at Epsom.
Seamie Heffernan was always in the perfect spot on the beautifully bred daughter of Galileo, but the passage of 11-4 favourite The Fugue, who finished a luckless third, left her owner Lady Madeline Lloyd Webber close to tears.
O'Brien was due to run six but pulled Kissed out an hour before the race on account of the quick ground. Was, out of a half-sister to Derby winner New Approach, then maintained his clean sweep of the British Classics this season - with odds-on favourite Camelot to come in the Derby.
Outsider Nayarra set only a pedestrian pace and those at the back, including the William Buick-ridden The Fugue, began to stack up in behind. The jockey was lucky to stay on board at one point as Betterbetterbetter chopped the favourite for room, and then Maybe was also interfered with.
Heffernan kept out of trouble in third position tight on the rail and kicked on two and a half furlongs out. Vow had her chance but could not quicken, while Shirocco Star and The Fugue began to make relentless progress. Was held on by a neck from Shirocco Star, with another half a length back to the favourite.
It was a fourth Oaks win for the master of Ballydoyle, but his first since Alexandrova in 2006. Joseph O'Brien was banned four days (June 15-18) for careless riding on Maybe, along with Darryll Holland on the runner-up.
The winning trainer said: "Seamus gave her a lovely ride. She came on lovely from her first run, so we were delighted. She's a very good-looking filly with a great pedigree. He's a great fellow, Seamus, a world-class jockey. He knows all these horses inside out and nobody deserves it more.
"We had been very happy at home with her in the spring, but she was coming up the gallop behind another horse whose shoe flew off and cut her above the knee. That delayed her and we were worried she'd miss the Classics."
Heffernan added: "This is massive, it means an awful lot. I've been runner-up in the Derby twice and I'm very lucky to get to ride in all these big races, usually with chances. We had a good position and our one worry was her lack of experience, but she's improved a lot since her last run."
The Fugue's trainer John Gosden said: "She was badly run into and was lucky not to go down. I've never been a bad loser, but you have to say she was unfortunate. It was a very messy race and she did well to get to where she did in the end. She ran a game race, but she just ran out of ground."