London 2012 chairman Lord Coe on Friday called for a zero tolerance policy towards drugs cheats a day after U.S. 400m Olympic champion LaShawn Merritt's ban against competing in next year's Games was overturned.

Merritt won a case in the Court of Arbitration for Sport (CAS) after challenging the International Olympic Committee's (IOC) controversial rule which states that anyone banned for doping for sixth months or more should miss the next Olympics.

Italian Flavia Pennetta stunned world number one Caroline Wozniacki with a fierce 3-6, 6-0, 7-6 (7/2) comeback in the quarter-finals of the China Open on Friday.

The Dane looked to be in control before Pennetta began a fightback, winning the second set to nil, and dominating a third set tie-break.

Dutch winger Arjen Robben has undergone successful surgery to remedy a troublesome groin problem, his club Bayern Munich confirmed on Friday.

Robben had been left "frustrated" after the injury flared up recently ruling him out of the Netherlands' forthcoming Euro 2012 qualifiers.

Former world number one Dinara Safina has retired from professional tennis, her elder brother Marat told media on Friday.

"Dinara (Safina) has decided to end her career," Safin said. "She has taken the decision relatively well. She considers it just to be the end of a period in her life."

Barcelona coach Josep Guardiola says he does not want a long-term contract with the European champions because he needs to feel free to decide his future so as to perform at his best.

The 40-year-old has preferred to sign one-year contract extensions since he was promoted from Barcelona's B team in June 2008 to replace Dutchman Frank Rijkaard in charge of the senior team.

Defending champion Rafael Nadal fought off a spirited challenge from Colombia's Santiago Giraldo to reach the semi-finals of the Japan Open on Friday.

The former world number one, playing his first ATP tournament since losing in the U.S. Open final last month, struggled to break Giraldo's serve in the first set and needed a tie-break to set him up for a 7-6 (8/6), 6-3 win.

Seven-time Formula One world champion Michael Schumacher believes fellow German Sebastian Vettel will savor his second crown as much as the first if he wins the title in Japan on Sunday.

Vettel, who needs to finish just 10th this weekend at Suzuka to become the youngest two-time champion in Formula One history, won the 2010 championship in the last race in Abu Dhabi in a nail-biting finish to the season.

World number one Novak Djokovic has withdrawn from next week's Shanghai Masters after failing to recover from a troublesome back injury, organizers said Friday.

Djokovic apologized for the pull-out, which deprives Shanghai of another star name after Roger Federer decided to skip the tournament to rest and deal with nagging injury problems.

Russia's big spenders Anzhi Makhachkala are reportedly trying to convince Manchester City's disgruntled striker Carlos Tevez to join recent signing Samuel Eto'o at the free-spending Caucasus side.

The Tvoi Den daily said Anzhi felt Tevez was there for the taking after his dramatic spat with City manager Roberto Mancini resulted in a two-week suspension for the Argentine star.

The father of Manchester United and England striker Wayne Rooney was among nine men arrested on Thursday over betting irregularities in a Scottish Premier League match, police sources said.

Wayne Rooney senior, 48, was detained at his home in Liverpool along with another seven people arrested in the city.