The 9-4 favourite Sariska got her head in front at the line to win the Epsom Oaks for jockey Jamie Spencer and trainer Michael Bell.
Sariska fought it out with Midday in the last furlong but had to wait on a stewards inquiry before taking the win.
Spencer took the filly to the front two furlongs from home and although she idled momentarily, she showed great determination for victory.
It gave Bell another Epsom Classic after Motivator won the 2005 Derby.
Johnny Murtagh on Perfect Truth made much of the running before fellow Irish raider Oh Goodness Me took over into Tattenham Corner but Sariska soon kicked for home
Although both Midday and the third-placed finisher High Heeled looked dangerous in the closing stages, Sariska held on well.
Bell said: "She's always shown us huge potential at home and ever since the day she started working I thought she was a star.
Sariska owner praises team effort
"She fulfilled all my expectations and we're so thrilled to have her. It is a huge thrill to win this race and I'm very lucky to have been given the chance to train her.
"It's a lonely place out in front, especially for a filly so inexperienced, but the post came in time."
Spencer added: "She's done it well, travelled well and is tough and game.
"I ended up in front a bit too early as she idled a bit in front, but these days are very special."
Earlier, the Sir Michael Stoute-trained Ask won a closely contested Coronation Cup in a photo finish from Youmzain from the Mick Channon yard.
The pair fought out a tremendous finish with last year's Oaks winner Look Here but the 5-1 shot, ridden by Ryan Moore, took it by a nose.
Frozen Fire set the early pace but Ask, the winner of last month's Yorkshire Cup settled in behind and challenged Johnny Murtagh's mount. When he faded, Youmzain and Look Here took up the challenge and ensured a tense finish.
"We never had any luck with him last year and although this wouldn't be his ideal track we had to take a chance," said Stoute afterwards.
Investec Oaks (1m 4f)
1. Sariska (J P Spencer) 9-4 Fav 2. Midday (T P Queally) 5-1 3. High Heeled (M Hills) 33-1 10 ran
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