- Associated Press - Wednesday, January 25, 2012

MELBOURNE, AUSTRALIA (AP) - The challenge system is proving, well, challenging for the top men at the Australian Open.

No. 4-ranked Andy Murray asked for five line calls to be reviewed by video technology in his quarterfinal against Kei Nishikori on Wednesday and failed on every one. No. 2 Rafael Nadal and No. 6 Tomas Berdych challenged a combined 20 calls the previous evening and got eight right.

Nadal was infuriated at 5-5 in the first-set tiebreaker when he tried to challenge a call after he had returned a shot, only to be told by umpire Carlos Bernardes he was too late.

The Spaniard later explained that he was more upset that Bernardes hadn’t overruled the call _ television replays showed the ball was clearly long.

Nadal believes the challenge system, which allows players three incorrect challenges per set, has discouraged umpires from intervening on line calls.

“They are there to make something, not just to call 15-all or 15-30 all the match,” he said. “That’s the only thing I’m unhappy about.”

He was a bit more pointed during the match when he said to Bernardes in Spanish: “You’re not here as a spectator.”

Nadal isn’t doing too badly on his challenges. He has been right with seven of 16 in his five matches so far for a 43.8 percent success rate.

Murray has managed to get five right from 22 for a miserable 22.7 percent, with Roger Federer _ who isn’t too keen on the system _ on three from eight. Of the men’s top four, Novak Djokovic is the most accurate with an accuracy rate of exactly 50 percent.

Aussie teenager Bernard Tomic has been one of the least accurate at Melbourne Park. In his four matches, he challenged 24 times and only had the call overturned on 3 occasions.

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ON A ROLL: Forget Novak Djokovic’s 43-match unbeaten streak to start the 2011 season. Esther Vergeer, the top women’s wheelchair player in the world, hasn’t lost a singles match in nine years.

After her win in the first round of the eight-woman wheelchair event at the Australian Open on Wednesday, the 30-year-old Dutchwoman extended her winning streak to 442 matches. The last time she lost a singles match was in January 2003.

“Won my match against Annick Sevenans today. Tomorrow I will play Sabine Ellerbrock, and of course doubles starts then as well,” Vergeer tweeted after the match.

Vergeer has been so dominant for so long in wheelchair tennis, she’s won practically ever Grand Slam tournament she’s ever entered. She’s captured 13 Grand Slam singles titles, including four Down Under, and 15 Grand Slam doubles trophies _ her only loss coming in the 2010 French Open final to Daniela Di Toro and Aniek van Koot.

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