Clijsters putting friendship on hold at U.S. Open

Serbia'a Ana Ivanovic has been one of the feel-good stories of this year's championship. The former world number one has been struggling for the past year but is suddenly starting to rediscover her best form.

Clijsters has been following Ivanovic's comeback closely and wants her to do well, but only to a point. The pair play each other at the U.S. Open on Sunday with a quarter-final berth at stake.

The odds are stacked in the Belgian's favor. She is a two-time winner of the championship and has won her two previous matches against Ivanovic.

She is also in great form, winning her first three matches in straight sets, but still working hard to perfect every part of her game.

"I feel like I'm close. It's only a matter of a few little details I think in my game that I just want to improve," Clijsters said.

Venus Williams, also a two-time champion in New York, plays Israeli 16th seed Shahar Peer on Sunday, having won all five of their previous encounters and hoping to continue her streak.

"I've always had a little bit of the upper hand, so hopefully that will give me a little bit of advantage in the next match," Williams said.

Rafa Nadal and Andy Murray, drawn to meet each other in the semi-finals, are also back in action Sunday, playing in their third-round matches since they started two days after the women.

Both men won their first two matches in straight sets and are firm favorites to continue on with Nadal playing Frenchman Gilles Simon and Murray up against Stanislas Wawrinka.

"He's a very, very difficult player," Murray said of Wawrinka. "He's had a lot of close matches with top players before so I'm going to have to play very well to win that one."

(Editing by Frank Pingue)