Djokovic headlines at night; the Williamses, Madisons look for wins
A Serena-Vika quarterfinal looms
With Azarenka rounding into form and looking as close to her best as we've seen in a year, a possible renewal of the rivalry that dominated women's tennis for two years is just a round away. But first, the business of the fourth round. Azarenka opens play on Rod Laver Arena against last year's finalist No. 11 Dominika Cibulkova. The Slovakian has been completely under the radar as she's quietly made her way into the second week with just the loss of one set. Azarenka leads the head-to-head 7-2 and is 6-0 on hard courts, though they have not played since 2012. The way Azarenka has been moving into and out of the corners, Cibulkova is going to have a big hitting day to push her off her game.
Serena follows on RLA with a rematch against No. 24 Garbine Muguruza. The young Spaniard famously handed Serena her heaviest loss at a Slam last year at the French Open. Looking back on that match, Muguruza said she played her absolute best tennis on that day. Much like Serena, Muguruza's first week was equal parts dominant and shaky. She finished each of her three matches with 6-0 bagel sets but has had to go the full three sets in her last two rounds. Serena overcame a slow start in her last match against another youngster, Elina Svitolina, before rolling to a 4-6, 6-2, 6-0 win.
Venus Williams looking for her first Slam quarterfinal since 2010
Venus looks to snap her three-match losing streak to No. 6 Agnieszka Radwanska (first night match, Rod Laver Arena). Venus has taken three heavy losses to Radwanska over the last few years, including a 6-4, 6-2 loss in the Rogers Cup final last summer. But all signs point to this match being different. As opposed to their last three meetings, Venus is fit and healthy. Nor should fatigue be an issue after her big comeback against Camila Giorgi in the third round, where she rallied from a set and 2-5 down to win in three sets. She'll need a good serving day to avoid getting into protracted rallies with the Pole, who has been dominant through the early rounds. She's lost just nine games in three matches.
Madison vs. Madison for a spot in the quarterfinals
Two fourth round debutantes face off with a major prize on the line: a spot in their first Slam quarterfinal. No. 35 Madison Keys comes in as the favorite after ousting No. 4 Petra Kvitova in the third round. No. 64 Madison Brengle is riding a wave of confidence after rolling into the fourth round with just one set lost. Her run has been nothing short of surprising. This is Brengle's first Australian Open main draw appearance since 2008 after falling in qualifying the last six years.
The match will be a contrast of styles (third match, Margaret Court Arena). Brengle is consistent and solid off the baseline, while Keys is the big-hitter with weapons. Brengle mixed things up nicely to frustrate another young big-hitting American in CoCo Vandeweghe in her last match, and she'll look to do the same against Keys.
More matches to watch
Kei Nishikori  vs. David Ferrer  (third match, Rod Laver Arena): How will Ferrer recover after a grueling four-set win over Gilles Simon in the last round? He struggled physically to finish the match and then revealed a bloody sock afterwards. He is on a four-match losing streak to Nishikori.
Milos Raonic  vs. Feliciano Lopez  (5 p.m. local time, Hisense Arena): If Lopez pulls off the upset he'll become the oldest man to reach the quarterfinals in Melbourne since Andre Agassi in 2005. Raonic is looking to make his best result at the Australian Open, having lost in the fourth round twice. The two have split their head-to-head, though Raonic has won their only meeting at a Slam at the 2013 U.S. Open. You have to favor Raonic here. He has torn through the first week without losing a set and he's only been broken once.
Novak Djokovic  vs. Gilles Muller (second night match, Rod Laver Arena): Though they've never faced each other it's hard to imagine the Serb having any trouble with Muller. His return of serve is just too good. Muller, 31, has lost just one set through his first three matches, booking his best Australian Open performance with a straight set win over John Isner in the third round.
Stan Wawrinka  vs. Guillermo Garcia Lopez (1:15 p.m. local time, Margaret Court Arena): Wawrinka will be looking for revenge over the Spaniard, who knocked him out of the first round of the French Open last year. Wawrinka leads the head-to-head 4-3.