Odds-on favourite Master Minded suffered a shock defeat in the Seasons Holidays Queen Mother Champion Chase at the Cheltenham Festival today, finishing only fourth behind the impressive winner, Big Zeb.

Master Minded, winner of this race for the past two years, never looked to be travelling as well as he had done in the past during the contest, and Big Zeb forged ahead of him before the final fence and galloped away strongly up the hill to win.

Nine-year-old Big Zeb, trained in Ireland by Colm Murphy, who won the Champion Hurdle here with Brave Inca in 2006, fell in the Champion Chase last year. And although the son of Oscar has won several big races in Ireland, he has never performed well in Britain and punters let him start at 10-1. Today was different, however, and Barry Geraghty galvanised him to commanding victory over Forpadydeplasterer, also trained in Ireland but ridden by AP McCoy.

Paul Nicholls, trainer of Master Minded, said: “We were beaten fair and square. I was concerned with the drying ground over the past couple of days and Ruby said he didn’t let himself down. I could see that, too, after a couple of fences. He is a big, heavy horse and on ground like this something just stops him letting himself down. He is a hard horse to train, unlike Kauto Star.

“As Ruby said, the horse has won two Champion Chases and today we have a new champion — that’s what racing is all about.”

Barry Geraghty doubled up with the Nicky Henderson-trained Spirit River in the next race, the Coral Cup, while Ruby Walsh gained a little compensation by taking the Fred Winter Juvenile Novices’ Hurdle on Sanctaire. Trained by Paul Nicholls, Sanctaire is a recent French import and absolutely bolted up.

Ruby wasn’t the only Cheltenham winner in the Walsh family. His sister Katie secured a first Festival winner in the day’s opener, the four-mile National Hunt Chase, on Ferdy Murphy’s Poker De Sivola. Unusually, two female jockeys battled it out at the finish — Katie defeated Nina Carberry (Becauseicouldn’tsee) by two lengths.

“”I’m lost for words. It’s definitely the best day of my life,” said Katie, 26, who used to event at three-star level before she decided to concentrate solely on racing.

Another amateur rider didn’t have such a dream result. Sam Waley-Cohen and Long Run, favourites for the RSA Chase, were beaten into third by Davy Russell and Weapon’s Amnesty, with Long Run proving that three miles is too far for him.