Favourite Annie Power, ridden by Ruby Walsh, powered to victory in the Champion Hurdle at Cheltenham.
The eight-year-old fell in the Mares' Hurdle last year but led from start to finish, the second of three wins for Walsh, 36, on a remarkable opening day.
Nicky Henderson's My Tent or Yours, in his first race for 703 days, was four-and-a-half lengths adrift in second.
Nichols Canyon was a head back in third, which meant trainer Willie Mullins claimed first and third.
Annie Power is only the fourth mare to win the Champion Hurdle and the first since Flakey Dove in 1994.
She was only entered into the two-mile showpiece, at a cost of £20,000, following an injury to last year's winner Faugheen, a Mullins stablemate also owned by Rich Ricci.
After recording his fourth Champion Hurdle success, an emotional Walsh said: "She deserved it. She's a great mare. It was a great performance.
"I knew halfway up the run-in she would win. It was brilliant, a great feeling."
Three horses die
Three equine fatalities marred the opening day as The Govaness, Pont Alexandre and Rezorbi all lost their lives.
Seven-year-old mare The Govaness died after a fall during the Mares' Hurdle.
The eight-year-old Pont Alexandre, trained by Mullins and owned by Ricci, suffered a fatal injury in the National Hunt Chase Challenge Cup.
Rezorbi died after falling in the final race of the day, the Novices' Handicap Chase.
A statement from the British Horseracing Authority read: "Our thoughts are with the owners, trainers and all the staff who have cared for these horses.
"We record and monitor all injuries and fatalities that occur on the racecourse to provide a benchmark from which the industry continually strives to reduce injury rates.
"Over the last 20 years, the equine fatality rate has fallen by a third - and in 2015 was the lowest on record, falling to just 0.18 per cent of runners."
Arkle Challenge Trophy
The Walsh-Mullins combination triumphed with odds-on favourite Douvan, who was a clear winner by seven lengths.
Vaniteux's challenge ended after a bad mistake at the second-last gave Nico de Boinville no chance of staying in the saddle, while Baltimore Rock came down independently at the same fence when at the rear.
Walsh powered up the hill to secure a second successive Cheltenham victory on Douvan following the Supreme Novices' Hurdle victory last year.
Sizing John once again had to play second fiddle, filling the runner-up spot for the fourth time in his career, while Fox Norton ran on to take third.
David Pipe's seven-year-old Un Temps Pour Tout got the better of 2014 winner Holywell after a good battle from three out.
There was little between them turning for home with two to jump, but the 11-1 shot pulled away up the hill under Tom Scudamore to win by seven lengths.
All the jockeys involved in the race received a one-day ban for anticipating the start.
Walsh and Mullins completed a first-day treble when Vroum Vroum Mag claimed the fifth race of the afternoon by two-and-three-quarter lengths.
She travelled smoothly in midfield for Walsh before cruising to the front at the last and powering clear from outsider Rock On The Moor, with Legacy Gold half-a-length away in third.
It was an eighth successive victory in the race for Mullins, all but one of which have been ridden by Walsh, who now has 48 winners at Cheltenham.
BBC racing correspondent Cornelius Lysaght:
"Congratulations to the Ricci/Mullins/Walsh axis for chalking up a memorable hat-trick, but, with respect, I think it has to be considered good news for the sport that they didn't prove completely invincible in the day's Grade One races, with Min being turned over spectacularly by Altior in the Supreme Novices Hurdle.
"It gave a message to their opponents that despite the extraordinary level of expensively-assembled talent at Mullins HQ, things don't always go right even for them. Phew. Annie Power and Vroum Vroum Mag were fantastic but Douvan's display was even better."