Finian's Rainbow won the Queen Mother Champion Chase as record-breaking trainer Nicky Henderson and jockey Barry Geraghty claimed a remarkable hat-trick at the Cheltenham Festival.
Henderson, who saddled four winners for a new Festival record of 44, saw his charge pip defending champion Sizing Europe in a controversial finish.
The pair had to swerve late to avoid the final fence after an earlier fall.
Henderson and Geraghty also combined for wins with Simonsig and Bobs Worth.
But the Gloucestershire course's mood was again dampened by the death of two horses, following three fatalities on the opening day.
Featherbed Lane, trained by Philip Hobbs, sustained a broken leg in the Coral Cup and the Brian Ellison-saddled Abergavenny also died after the same race.
The Champion Chase was the feature race of Ladies' Day and Sizing Europe, trained by Henry de Bromhead, was the 4-5 favourite to retain the crown.
But Finian's Rainbow edged the champion in a fierce battle on the longer than usual run-in after the field were diverted around the final fence following Wishfull Thinking's earlier fall at the jump, which saw rider Richard Johnson catapulted over the barrier into spectators.
The leading pair were diverted around the obstacle and Sizing Europe appeared to lose momentum under jockey Andrew Lynch.
De Bromhead said his rider felt the controversial decision to cordon off the last fence proved vital in the race's outcome.
"We were beaten which is about all I can say on the matter," said the trainer. "Andrew didn't know he was going to have to miss the last.
"We haven't really discussed it but he just said 'the last cost me the race'."
A jubilant Geraghty said: "It's a brilliant day - you dream of days like this. I'm genuinely so delighted for [owner] Michael Buckley.
"He's had a good few disappointments this season, but he's had patience with this fellow [Finian's Rainbow] and I really am delighted for him."
One of the week's biggest talking points had been Henderson's bid to become the Festival's most successful trainer.
With 39 successes under his belt, he needed only two more winners to better the record 40 saddled by Fulke Walwyn between 1946 and 1986.
Sprinter Sacre's win in the Arkle Challenge Trophy on Tuesday had moved Henderson alongside Walwyn before he smashed the record in style with four winners on Wednesday.
There was a lot of hype surrounding Simonsig before the second race, the Neptune Novices' Hurdle, and the grey did not disappoint as it romped to a seven-length victory over Felix Yonger.
After clinching the record, Henderson said: "It's nice. But I'm lucky we've had good horses all the way through, good owners and a good team back home."
However, six-year-old Simonsig's bid was helped by second-placed Cotton Mill refusing the penultimate obstacle, sending jockey Denis O'Regan hurtling from the saddle.
The winning combination of Henderson and Geraghty was celebrating a double when Bobs Worth won the RSA Chase. The hotly tipped Grands Crus, which was switched from Gold Cup, faded badly on the straight to finish fourth.
Henderson completed a quadruple when 40-1 shot Une Artiste won the Juvenile Handicap Hurdle, which followed Son Of Flicka's win in the Coral Cup.
Rebecca Curtis celebrated her maiden festival winner when favourite Teaforthree clinched the opening Diamond Jubilee National Hunt race on Ladies' Day.
Ridden by top amateur JT McNamara, the 5-1 chance sat handily throughout the four-mile test and sailed over the final fence to burst clear of long-time rival Four Commanders.
Nina Carberry's ride lost momentum following a laboured jump on the last, which allowed Harry The Viking, part owned by Manchester United football manager Sir Alex Ferguson, to clinch second.
"Seeing my first winner was a very special feeling - it brought a tear to my eye," said Curtis afterwards.