Wozniacki and Azarenka face off, more Day 4 matches to watch

MELBOURNE --Here are the matches to watch on Day 4 of the Australian Open. Play begins on all courts at 7pm ET on ESPN2. Click here for the order of play, and

MELBOURNE --Here are the matches to watch on Day 4 of the Australian Open. Play begins on all courts at 7pm ET on ESPN2. Click here for the order of play, and see the full TV schedule here.

Caroline Wozniacki and Victoria Azarenka square off 

The best match of the day didn't even earn a spot on Rod Laver Arena. The two former No. 1s will face off in the first night match on Margaret Court Arena in a match that serves as a big hurdle for No. 8 Wozniacki and an important litmus test for two-time champion Azarenka. A win for Azarenka would not only set herself up for a deep run in Melbourne, but also serve as a pronouncement that she's playing near her pre-injury level. After spending a significant portion of the 2014 season on the sidelines due to a foot injury, Azarenka is down to No. 44 in the rankings. 

Mailbag: Sharapova survives, nearly edges Russian qualifier to advance

​Wozniacki leads the head-to-head 4-3 but two of their last three completed matches have gone the distance. 

"I know she's very dangerous," Azarenka said. "We always had some of tough matches. I would like to focus on myself and what I can do to build my game, to prepare as best as I can, and just compete. That's my key word for this tournament: Compete."

Serena Williams plays Vera Zvonareva

This was a Wimbledon final five years ago back when Zvonareva finished the season at No. 2. Now down to No. 203 after suffering a shoulder injury, the two face off in the second round. 

​CoCo Vandeweghe and Madison Keys go for Aussie upsets

Former AusOpen finalist Hewitt gets win reminiscent of the 'good old days'

It won't be easy but it can be done. Madison Keys plays No. 29 Casey Dellacqua (third match, Margaret Court Arena) and CoCo Vandeweghe goes under the lights on Rod Laver Arena to take on Australia's best, No. 20 Sam Stosur (second night match, Rod Laver Arena.) Vandeweghe beat Stosur in their last match 5-7, 7-5, 7-5 in Miami last year. Keys beat Dellacqua in their only meeting two years ago here in the first round 6-4, 7-6 (0). 

Novak Djokovic and Stan Wawrinka look to continue their form

Both men blitzed through their opening rounds and should do the same on Thursday. Djokovic plays No. 88 Andrey Kuznetsov (third match, Rod Laver Arena) and Wawrinka plays No. 194 Marius Copil (second match, Margaret Court Arena).

More matches to watch

Sharapova saves two match points to beat Russian qualifier Panova

Gael Monfils [17] vs. Jerzy Janowicz (fourth match, Hisense Arena): Two of the most explosive, unpredictable players on one court. Your guess is as good as mine as to what will happen. 

Kei Nishikori [5] vs. Ivan Dodig (first match, Hisense Arena): Nishikori has won their last two matches but Dodig can be a tough opponent. 

Steve Johnson vs. Santiago Giraldo [30] (first match, Court 15): This is a big opportunity for Johnson to make the third round of a major for just the second time in his career. 

Venus Williams [18] vs. Lauren Davis (first match, Margaret Court Arena): A win would put Venus into the third round for the third straight Slam. 

John Isner [19] vs. Andreas Haider-Maurer (first match, Show Court 2): Isner tries to back up his clean win in the first round, where he only had to play one tiebreaker. 

Petra Kvitova [4] vs. Mona Barthel (third match, Hisense Arena): Kvitova had a non-nonsense first round win but we still feel the need to keep an eye on her. Barthel can be tough to beat if she finds her rhythm.