KEY BISCAYNE, Fla. — Since arriving on Key Biscayne, Andy Roddick has played H-O-R-S-E with D-Wade, hung out with T.O. and helped organize a charity event to benefit Chilean earthquake victims.

He's also squeezing in a little tennis. Roddick advanced to the quarterfinals of the Sony Ericsson Open by beating Benjamin Becker 7-6 (4), 6-3 on Tuesday.

Seeded sixth, Roddick improved to 23-4 this year, and he leads the men's tour in wins. He seeks his first Key Biscayne title since 2004 and hopes to prevent a potential showdown Sunday between Roger Federer and Rafael Nadal.

Roddick's hoops contest against Dwyane Wade was for laughs, as were brief get-togethers with Terrell Owens, a friend and tennis fan. The Chilean benefit is a doubles match in which Roddick will take part Saturday — the evening before the men's final.

"Even if things go great and I'm in the final, I'll still play Saturday, just because it's necessary and what needs to happen," he said. "It's a bigger cause than my tournament."

Nadal, who could face Roddick in the semifinals, advanced by beating fellow Spaniard David Ferrer 7-6 (5), 6-4. Three-time champion Venus Williams became the first women's semifinalist by defeating No. 6-seeded Agnieszka Radwanska 6-3, 6-1.

To get past the unseeded Becker, Roddick rallied on the strength of his dominating serve. He dug out of a 1-4, love-40 hole in the first set and won 34 of his final 39 service points, including all six in the tiebreaker.

Roddick said experience helped with the turnaround.

"When things aren't going my way, I'm probably better now," he said. "Six years ago on the court my highs were a lot higher, and the lows were a lot lower. If I would have gotten down early, I don't know if I would have stayed the course."

A big serve helps, too. When Roddick found himself in another hole serving at 4-5, love-30, he responded with three service winners and an ace, all in the 133- to 135-mph range.

"It's nice at love-30 to be able to make some first serves," he said.

Roddick made another one on match point, closing out the victory with his seventh ace of the match and his 343rd of the year, second-most on the tour. He has been broken only once through three matches and next plays No. 33-seeded Nicolas Almagro, who eliminated No. 27 Thomaz Bellucci 6-4, 3-6, 7-6 (3).

The woman with the best chance to beat Venus Williams at Key Biscayne watched the women's quarterfinals from the photo pit. Serena Williams had no camera but used her connections to secure a front-row seat as she watched her sister beat Radwanska.

Top-ranked Serena has been sidelined by a knee injury since winning the Australian Open in January. In her absence, Venus has become the woman to beat as she bids for her fourth Key Biscayne title and her first since 2001.

"When I'm executing and playing my best, it's great," Venus said. "It feels good, and I feel like I'm definitely dictating the points and that I don't give my opponent as many chances to have a say."

The oldest women's quarterfinalist at 29, Venus is the hottest player on the WTA Tour. She has won 14 matches in a row, and two more would give her three consecutive tournament titles for the first time since 2002.

In the men's fourth round, American Mardy Fish retired with a sciatic nerve injury trailing Mikhail Youzhny 6-1, 1-0. The injury occurred when Fish took a tumble in the first set, causing discomfort from his back to his calf.

"I don't think I've ever felt that much pain on a tennis court," said Fish, who is coming back from knee surgery last September.

No. 8 Jo-Wilfried Tsonga earned a shot at Nadal in the quarterfinals by beating No. 12 Juan Carlos Ferrero 6-2, 6-2. The fourth-seeded Nadal, seeking his first Key Biscayne championship and his first title anywhere in 10 months, punctuated his win over Ferrer with a nifty leg kick-uppercut combination.

No. 5 Robin Soderling defeated No. 9 Fernando Gonzalez 6-0, 6-7 (3), 6-2.

The No. 3-seeded Williams hit eight aces and lost only five points on her first serve. She broke five times, including in the pivotal eighth game, when Radwanska had consecutive double-faults and then hit a 62-mph knuckleball serve that Williams pounced on to whack a winner.

Williams struggled with her backhand but won 15 of 19 points at the net.

"I play my best game when I'm more aggressive, because that's my style," she said. "Others don't play as well as aggressive, because that's not their style. It just seems to be better when I move forward, and I try to do that."