Roksana emerged victorious in the OLBG Mares' Hurdle at Cheltenham after red-hot favourite Benie Des Dieux crashed out at the final flight.
Trainer Willie Mullins had claimed this prize nine times in the 11 previous years it had been run - with the remarkable six-time winner Quevega joined on the roll of honour by Glens Melody, Vroum Vroum Mag and Benie Des Dieux.
Having already won the Supreme Novices' Hurdle with Klassical Dream and the Arkle Trophy with Duc Des Genievres, Mullins looked to have outstanding claims of completing an opening-day treble, with Benie Des Dieux the 10-11 favourite to successfully defend her crown.
Everything went according to script for much of the two-and-a-half-mile journey, with Benie Des Dieux always travelling strongly while her stablemate Stormy Ireland cut out the running.
Ruby Walsh eased Benie Des Dieux to the front before the home turn and she was well in command when she crashed through the final hurdle and came to grief - an almost carbon copy of the fall suffered by Annie Power for the same connections in this race four years ago.
Her exit saw the Dan Skelton-trained and Harry Skelton-ridden Roksana left in front and she managed to hold the rallying Stormy Ireland at bay by two and a quarter lengths.
Another Mullins runner, Good Thyne Tara, was third.
D'Allen delivers stunning performance in Champion surprise
Espoir D'Allen produced a coming-of-age performance to claim a brilliant victory in the Unibet Champion Hurdle at Cheltenham.
A field of 10 runners went to post for the two-mile showpiece and much of the pre-race chat focused on dual winner Buveur D'Air being taken on by Irish mares Apple's Jade and Laurina.
The Gordon Elliott-trained Apple's Jade was the marginal favourite at 7-4 and challenged last year's runner-up Melon for the lead throughout, after Buveur D'Air provoked gasps from the grandstands as he crashed out in the early stages.
However, it was clear some way from home that she was in trouble and as she dropped away racing down the hill, Melon remained in front, with his stablemate Laurina travelling strongly in his slipstream.
But all the while Mark Walsh was biding his time aboard 16-1 shot Espoir D'Allen - who had won each of his three previous starts this season for trainer Gavin Cromwell - and he shot clear from the home turn to seal a hugely-impressive victory by 15 lengths.
Melon boxed on to finish second again, with 80-1 shot Silver Streak in third and Laurina fourth.
Buveur D'Air - bidding to become just the sixth horse in history to win the Champion Hurdle three times - appeared none the worse for his mishap and actually finished upsides the winner crossing the line.
Bear necessity in Ultima triumph for Henderson
Beware The Bear claimed top honours in the Ultima Handicap Chase at Cheltenham.
Trained by Nicky Henderson and ridden by Jerry McGrath, the nine-year-old was a 10-1 shot for the first handicap of the Festival in a fiercely-competitive field of 24 runners.
For much of the way it looked like Up For Review might give Willie Mullins his third winner of the afternoon as he travelled powerfully on the heels of the leaders running down the hill.
However, he made a mistake three fences from the finish and his effort soon petered out.
Beware The Bear - a winner at Cheltenham in January - was in the lead at the top of the home straight and while Sue Smith's Vintage Clouds finished strongly, Henderson's inmate had just enough in reserve to hold him at bay.
Nick Alexander's top-weight and Grand National contender Lake View Lad ran a fine race to finish third ahead of Lucinda Russell's Big River - another Scottish challenger - in fourth.
Duc Des Genievres dazzles in Arkle Trophy demolition
Duc Des Genievres ran out a facile winner of the Racing Post Arkle Challenge Trophy at Cheltenham.
With trainer Willie Mullins having already teamed up with Ruby Walsh to land the opening Supreme Novices' Hurdle with Klassical Dream, Duc Des Genievres was a 5-1 shot to follow up in the hands of Paul Townend.
The result was scarcely in doubt, with the six-year-old grey fencing fluently throughout the two-mile contest in behind the pacesetting Knocknanuss, before taking over the lead still full of running before the home turn.
Clondaw Castle briefly looked a threat, but soon weakened as Duc Des Genievres found another gear in the straight to leave his rivals trailing in his wake.
Us And Them came home best of the rest, but passed the post some 13 lengths behind the dominant winner.
Glen Forsa unseated Jonathan Burke early on, while 100-30 favourite Hardline never threatened to land a telling blow.
Klassical Dream rules supreme for Mullins and Walsh
Klassical Dream provided Willie Mullins with a record sixth victory in the Sky Bet Supreme Novices' Hurdle, the first race of the 2019 Cheltenham Festival.
It is 24 years since the winning-most trainer in Festival history first landed the traditional curtain-raiser with Tourist Attraction (1995), since when he has struck gold with Ebaziyan (2007), Champagne Fever (2013), Vautour (2014) and Douvan (2015).
This year Mullins fired a twin assault, with 6-1 shot Klassical Dream renewing rivalry with stablemate Aramon after the pair fought out the finish of a Grade One at Leopardstown last month.
Ruby Walsh - the most successful jockey in Festival history - always had Klassical Dream in prime position as he tracked the pacesetting Brandon Castle before taking over the lead racing down the hill.
It was clear rounding the home turn the five-year-old - who was at the forefront of a false start to the race - had his rivals in serious trouble and he powered up the hill to score by four and a half lengths under a jubilant Walsh.
The Olly Murphy-trained pair of Thomas Darby (28-1) and Itchy Feet (25-1) finished second and third respectively.
Mullins said: "It was a terrific performance and he is good horse. We took a risk running him on goodish firm ground at home, but we thought he had an engine on him.
"We debated whether to go for the other race (Ballymore Novices' Hurdle), but when we saw this rain coming we said we would come for this race. The forecast was a big thing once we knew this ground was coming.
"He was well within his own cruising speed. He looks a real good one on this type of ground. He is a very good horse.
"We came away from his work at the Curragh last week thinking he was one that was going to take a lot of beating, no matter what he came up against."
The winner was running in the colours of late owner John Coleman, and Mullins added: "It's a very poignant victory for us, as John had a lot of cheaper horses with us and then he retired and sold his business and said 'here is a few quid, go and buy me a Cheltenham horse' and this was the horse.
"Jo (wife) and his family are here, which is fantastic. It is a very emotional victory for us, which is fantastic. I'm delighted it happened for his family."
Murphy was delighted with the efforts of his pair.
He said: "I'm over the moon, they are two horses I've always held in high regard and they've finished second and third.
"I'm not someone who jumps up and down about finishing second and third, but it's my first full season and I've got to keep telling myself that - to have two in a Grade One alone is great.
"The rain hasn't helped either of them, they both want good ground. They were both given very good rides and unfortunately they've just bumped into a very good one.
"I'll definitely step one of them up in trip, whether we go two and a half at Aintree or wait for Punchestown, as we've beaten the rest of the Irish and I wouldn't be afraid to travel.
"I just wouldn't be mad to run on this ground again."