Petra Kvitova vs. Ana Ivanovic (first match, Rod Laver Arena):Ivanovic is a bit under the weather, but the 2008 Australian Open finalist has cruised through three rounds without dropping a set. The Serb has a 3-0 record against Kvitova, with all those victories coming during her reign as one of the WTA's best in 2008 and 2009. Times have obviously changed and the two haven't played in almost three years. The Kvitova of now is definitely not the Kvitova of then, and Ivanovic will need some help from the Czech (who can be error-prone) to have a chance to reach a Grand Slam quarterfinal for the first time since 2008. "It's just very exciting to be in a second week," Ivanovic said after Saturday's victory against Vania King. "That was a first step. It's nice to be able to achieve that. Now it's going to be tough matches, match after match. But I still believe I can do well. I'm just enjoying competing again. It's going to be tough, but I love challenges."
Serena Williams vs. Ekaterina Makarova (third match, Rod Laver Arena): The 56th-ranked Makarova has had a heck of a tournament, beating Kaia Kanepi (who won the Brisbane tune-up) and reducing seventh-seeded Vera Zvonareva to tears in a straight-set win in the third round. But on paper, this looks like a steamroll for the powerful Williams. Serena has had a few hiccups in Melbourne, so we still haven't seen the five-time champion hold her form from start to finish. This might be the match that knocks the last bit of rust off the wheels.
Maria Sharapova vs. Sabine Lisicki (first night match, Rod Laver Arena): This is a rematch of a Wimbledon semifinal last year, when Sharapova overcame 13 double faults to win 6-4, 6-3. Sharapova has been in devastating form, surrendering a mere five games through three rounds. Lisicki struggled in the heat in her first round and could benefit from a night match. Then again, her serve won't be as effective in the slower conditions. No reason to bet against the Russian here. She's been ruthless.
Novak Djokovic vs. Lleyton Hewitt (second night match, Rod Laver Arena): Can Hewitt play as well as he did Saturday, when he defeated Milos Raonic? That's the best the 30-year-old Australian has moved in years and he'll have to duplicate it to have a chance to grab even a set from Djokovic, who hasn't dropped more than five games in a match. Hewitt will have the crowd behind him and the fire still burns. Djokovic would do well to snuff out any belief by getting off to a strong start. Which is kind of his default setting these days. Jo-Wilfried Tsonga vs. Kei Nishikori (second match, Hisense Arena): Nishikori has had to work hard to get here, becoming the first Japanese man in the Open era to reach the fourth round of the Australian Open. The No. 24 seed came back from two sets down against Matthew Ebden in the second round and then played a taxing four-setter against Julien Benneteau. On the other hand, Tsonga has lost one set. The Frenchman's firepower will be a huge challenge for Nishikori, who will need his tired legs firing if he's to disrupt Tsonga's rhythm on the baseline.