CHELTENHAM, England (AP):

The Cheltenham Festival opened with a big upset yesterday when Rock On Ruby left odds-on favourite Hurricane Fly in his wake to win the Champions Hurdle, the day's standout race.

Hurricane Fly (4-6) was defending the title he won easily last year and looking to win his eighth-straight Grade One race, but left his challenge too late and finished third.

Rock On Ruby, an 11-1 shot trained by Paul Nicholls, shadowed long-time leader Overturn before taking the lead after the second-last fence and staying on up the hill to win by nearly four lengths.

"I was worried going to the last as he was pulling up a little bit, but he picked up again afterwards," jockey Noel Fehily said. "He (ran) very well on the day."

Overturn finished second with odds of 20-1.

Rock On Ruby's victory gave Nicholls - a serial champion trainer in Britain - his first win of a festival that he hopes will end with a famous triumph for his most famous horse, the veteran Kauto Star, in the showpiece Gold Cup race.

Ruby Walsh, who will be the jockey aboard Kauto Star, had a disappointing run on Hurricane Fly after staying near the back of the field for much of the 2- 1/2 -mile race.

"He was beaten too far out," Walsh said.

The day's other major race, the Arkle Challenge Trophy Chase, was won by Sprinter Sacre to give trainer Nicky Henderson a record-equalling 40th Festival winner.

dreadful show-off

"He is unreal," Henderson said of a horse who has been tipped to challenge for the Gold Cup next year. "More than anything, he's just a dreadful show-off and wants everyone to watch him. And he's worth watching frankly."

Walsh grabbed a winner in the Mares' Hurdle, the sixth of the day's seven races, when Quevega won it for the fourth time.

The four-day meeting, which is the jewel in the crown of British horse racing, continues today when Sizing Europe bids to retain his title in the Queen Mother Champion Chase.