MELBOURNE, Australia - The middle Sunday of the Australian Open sees both Serena Williams and Li Na in action, although arguably the pick of the top half matches involves two players slightly lower down the rankings.
Sunday, Fourth Round
Rod Laver Arena
 Serena Williams (USA #1) vs.  Ana Ivanovic (SRB #14)
Head-to-head: Williams leads 4-0
When Ana Ivanovic steps onto Rod Laver to face Serena Williams on Sunday afternoon she will be bidding to reach the quarterfinals at Melbourne Park for the first time since 2008. On that occasion the Serb went on to reach the final, however, if she wants to repeat the feat one of the performances of her career will be required.
In Williams, she is taking on a player at the very top of her game. Since losing to Sloane Stephens on her last visit, the American has posted a remarkable 77-3 win-loss record, reclaiming the French and US Open crowns in the process. This fine form has been carried over into 2014, where Williams has looked hungry for a sixth Australian Open title and first since 2010, dropping just 12 games thus far.
While not quite as serene, Ivanovic's progress has been impressive nonetheless; she won her first two matches comfortably before coming from a set down to defeat home favorite Samantha Stosur in the third round. Williams has won all four of the players' past encounters in straight sets - the most recent coming at the US Open in 2012 - and Ivanovic will need to serve well and stay aggressive, particularly on the forehand, if she is to stand a chance of causing the upset.
 Eugenie Bouchard (CAN #31) vs. [WC] Casey Dellacqua (AUS #120)
Head-to-head: first meeting
Melbourne Park has become a home away from home for Eugenie Bouchard this week. The Canadian's attacking style on court and girl-next-door charm off it has seen her build an army of loyal followers who have packed the outside courts during her opening three matches.
These acolytes, though, will have their loyalties tested when she makes her way onto Rod Laver for the first time. Her opponent, Casey Dellacqua, is the last remaining Australian in the draw, and has been a firm favorite in these parts ever since her irresistible run to the last 16 in 2008.
Last summer, Dellacqua was playing ITF events in Bendigo as she looked to resurrect a ranking that once stood as high as No.39. She impressed during a straight set dismissal of No.18 seed Kirsten Flipkens last time out and she will need more of the same if she is to derail the Bouchard bandwagon.
 Li Na (CHN #4) vs.  Ekaterina Makarova (RUS #22)
Head-to-head: Li leads 4-0
If past meetings are anything to go by, Ekaterina Makarova's chances of making it past last year's runner-up Li Na are slim. Li has won all four of their previous encounters, including a high-quality encounter at last year's US Open.
However, the Russian has historically saved her best tennis for this time of year - she made the quarterfinals in 2012 and 2013 - and since coming through a tough opening examination from Venus Williams has grown in confidence.
Li will present a different set of challenges and both the Russian's lefty serve out wide and big forehand will have to be firing on all cylinders once again. While Li has an enviable record Down Under, she has looked a little off-color so far and came within a point of a shock third round exit to Lucie Safarova on Friday.
Also on court...
In the day's other fourth round match, the in-form Angelique Kerber meets Flavia Pennetta, while in the doubles top seeds and defending champions Sara Errani and Roberta Vinci take on Australian wildcards Monique Adamczak and Olivia Rogowska.