!Picby Pete Bodo

MIAMI—It’s cloudy here this morning, but it ought to burn off and produce another day of blue skies. We’re down to the fourth round on the ATP side, and into the bottom half quarterfinals for the WTA. But the players will be hard pressed to top yesterday’s performances by Victoria Azarenka and Andy Roddick.

Here are the four Tuesday matches I find most intriguing:

Grigor Dimitrov vs. Janko Tipsarevic (No. 9): Every fourth round at a 128-draw tournament coughs up a few pairings that nobody would have predicted, and this is the outstanding one in the ATP draw. Dimitrov is a talented 20-year-old from Bulgaria, touted for so long as the “next” this one or “next” that one that it seems like he’s been around almost as long as Donald Young.

Tipsarevic has been very good sustaining his place at the outer edge of the Top 10, drafting (emotionally, at any rate) behind his countryman, world No. 1 Novak Djokovic. He’s beaten Dimitrov in their two previous meetings, but you can throw that out the window because of Dimitrov’s age. This will be good test for Tipsarevic: Dimitrov upset Tomas Berdych and could be on the cusp of the long-awaited breakout.

The pressure will be on Tipsarevic, but the feeling here is that Dimitrov is still too immature to take out two Top 10 players in the span of a few days. I'll be writing about this one later.

Serena Williams (No. 10) vs. Caroline Wozniacki (No. 4): After the performance Serena turned in yesterday against Slammin’ Sammy Stosur (Serena hit a career high 20 aces in just two sets), Wozniacki knows exactly what she’s up against.

The high-quality win by Serena has dispelled any doubt about her fitness, physical or mental, for the rigors of tour play after her long layoff. And hey, did you hear? Wozniacki is struggling. . . Well, that may play well on the Internet and in the papers, but Williams said in her presser yesterday that she’s not buying any of it—Wozniacki in her eyes is still the same player who finished as the year-end No. 1 in 2010 and 2011 but has yet to . . . never mind. You know what I was about to say.

These two have met three times, Williams prevailing in each match. Wozniacki has been talking about her plans to play a little more offense, and this would be an excellent time to put her words into action. I still like Serena to overwhelm the defensive Dane. I’ll be writing a Racquet Reaction when it ends tonight.

Gilles Simon (No. 13) vs. Andy Murray (No. 4): Murray dodged a bullet when Milos Raonic pulled out with an ankle injury, and he’s certainly going to have fresh legs. He’ll need them against Simon, who hasn’t lost a set here and is one of the few players on the tour who can match Murray in the defense department.

The problem for Simon is that Murray is that much better at switching to or starting out on the attack. That helps explain Murray’s 8-1 head-to-head lead. Simon is a kind of ATP barometer; unless he has a miserable day, if you beat him you’re entitled to thinking you’re playing well and have all of your vulnerabilities covered. Given Murray’s disappointing flame-out at Indian Wells, he needs a good performance here to call the early hard-court season an unqualified success. I think he'll handle Simon.

Maria Sharapova (No. 2) vs. Li Na (No. 8): It seems like the serving yips have once again descended upon Sharapova, which is bad news for her, given that Li has won their last four matches.

Li goes through enormous swings in productivity, but it's a good sign for her that this is her second quarterfinal in a row, and on a comparable court. This suggests that she’s in one of her “up” phases.
Li will be accustomed to the pace Sharapova will try to establish, because she’s coming off a three-set win over hard-hitting Sabine Lisicki.

I’ll be writing a post about this one, and my feeling going in is that Li’s mobility and smooth, compact game will give Sharapova fits once again. I’m picking Li.