What we learned from Wednesday's matches

9/4/2008 - Tennis

Ravi Ubha is providing instant analysis of each one of Wednesday's matches -- which feature Dinara Safina, Flavia Pennetta, Serena and Venus Williams, Andy Murray, Juan Martin del Potro, Rafael Nadal and Mardy Fish. Come back for the latest.

1. Safina has great recovery power: Before her fourth-round match against German Anna-Lena Groenefeld on Monday, Dinara Safina was in tears.

Exhausted after a grueling yet successful summer, Safina didn't know whether she'd even be able to show up on court. Calmed by her coach, Zeljko Krajan, the sixth seed proceeded and advanced comfortably.

She showed no residual effects Wednesday, easing past Italian Flavia Pennetta, 6-2, 6-3, in 1 hour, 11 minutes.

"Already yesterday I was practicing, and I had already a smile on the face," Safina said. "I was like, 'OK, now I can play and move. Now I can get only better so that slowly I'm getting back.'"

Safina gets one of the Williams sisters in the semis. She trails Serena 3-1, though she won their lone head-to-head in 2008, on clay. Safina has never faced Venus.

2. It's tough holding a lead: Andy Murray and Juan Martin del Potro can attest to that.

Whichever player lost, he'd be kicking himself, and in this case it was del Potro, whose 23-match winning streak ended with the 7-6 (2), 7-6 (1), 4-6, 7-5 defeat that took about four spellbinding hours.

Here's only a smidgen of what transpired: Del Potro, clearly the aggressor, failed to serve out the first set and twice blew a break lead in the fourth, at 2-0 and 4-3.

Murray was up a break in the first, couldn't serve out the second at 6-5 and led by a break in the third.

"I had my chance in the third set and let it slip," Murray said.

As the score indicated, there wasn't much to separate the young pair -- Murray turned 21 in May; del Potro will turn 20 on Sept. 23 -- who are sure to be rivals at the elite level for years to come. Both broke seven times, and Murray won five more points overall, 154-149.

3. 2008 is a vintage year: For the Williams sisters, that is. Like a fine California wine, their head-to-heads get better with the passage of time.

So good was their tilt at Arthur Ashe Stadium on Wednesday night -- the first time in 17 meetings Venus and Serena faced off in a Grand Slam quarterfinal -- the feisty New York crowd gave them a standing ovation during the second-set tiebreaker.

"I think intensity-wise, it was the best match of the tournament, and that includes the men," said 1989 U.S. Open champion Boris Becker, who is serving as an analyst for USA Network.

Avenging a defeat by Venus in a high-quality Wimbledon final in July, Serena put in a gritty display to prevail 7-6 (6), 7-6 (7) in 2 hours, 25 minutes. At the Bangalore Open in March, Serena triumphed in a dramatic semifinal, winning the third-set 7-6 (4).

It won't take a genius to figure out where the match swung. Venus, the elder of the sisters, failed to serve out each set and blew a total of 10 set points.

"I'm a very good closer, so today was, you know, I've never had a match like this in my life," Venus said. "I guess there's always a first."

4. Rafa knows how to protect his serve: Not armed with a big delivery, Rafael Nadal nevertheless knows how to protect his serve. Over five glorious sets against Roger Federer in the Wimbledon final, on grass, he dropped serve only once.

One round after getting broken four times by big-hitting Sam Querrey -- and facing 16 break points -- Nadal was broken only once by Mardy Fish in Wednesday night's (or is that Thursday morning's?) 3-6, 6-1, 6-4, 6-2 quarterfinal victory over another American, and one with a powerful serve.

It came in the second game and was the lone break chance he faced.

Nadal, who obviously backs up his serve much better than Fish, went 5-for-12 on break points and constantly threatened.

Ravi Ubha is a frequent contributor to ESPN.com.