MELBOURNE, Australia (AP) One big question ahead of the start of the third round Friday at the Australian Open is the state of Andy Murray's injured right ankle. And nearly as important, how Roger Federer will perform in his first major test - against Tomas Berdych - since returning from a six-month injury layoff.
The top-seeded Murray tumbled to the court at Rod Laver Arena, clutching his ankle and cringing in pain during the third set of his second-round match against No. 156-ranked Andrey Rublev on Wednesday.
''It just a little bit stiff just now,'' he said after the match. ''I don't think I've done too much damage.''
Murray held a practice session on Court 17 on Thursday afternoon and appeared to be moving freely. He is scheduled to play No. 31-seeded Sam Querrey in a Hisense Arena afternoon match.
Something that may have made Murray's ankle feel better later in the day was news that Novak Djokovic was upset in the second round by Denis Istomin. On opposite sides of the draw, they couldn't have met until the final, but Murray has lost five finals at Melbourne Park - four of them to Djokovic.
Here is a look at some of the other featured matches Friday:
FEDERER'S BIG TEST: Undoubtedly No. 10 Tomas Berdych will be 17-time Grand Slam winner Roger Federer's biggest challenge since returning from his left knee layoff. Federer, a four-time Australian champion, was tested from time to time in wins over qualifiers in his opening two matches.
The good news is that he holds a 16-6 career edge over Berdych, including all three times they've met previously at Melbourne Park. Federer is 5-0 in their most recent meetings.
''I did feel like I actually played him quite well in recent times, thanks for reminding me,'' Federer said. ''I just got to play on my terms and really be focused on my own service games to make sure I don't have any lapses there. I know I've got to lift my game a little bit.''
The pair will play the final night match on Rod Laver Arena.
BEATING THE TWINS?: Top-ranked Angelique Kerber beat Karolina Pliskova in the U.S. Open final, and will have a chance to beat the Czech player's twin sister, Kristyna, in the next major when the pair meet in an afternoon match at Rod Laver Arena.
Kerber has never played the 58th-ranked Kristyna.
Asked if it was ''weird'' to play twins, Kerber seemed perplexed by the question. ''I don't know if it's weird. I mean, the one is right and the other one is left-handed.''
For the record, Kerber and Kristyna are both left handed.
No. 4 Stan Wawrinka vs. No. 29 Viktor Troicki: U.S. Open champion and 2014 Australian winner Wawrinka beat Troicki in the second round at the Brisbane International two weeks ago, his seventh consecutive win over the Serbian player. Advantage Stan.
No. 7 Garbine Muguruza vs. No. 32 Anastasija Sevastova: 2016 French Open champion Muguruza lost to Sevastova in the second round at the U.S. Open last year in straight sets, but returned the favor at Tokyo a few weeks later.
No. 13 Venus Williams vs. Duan Yingying: Duan beat former top 20 player Vavara Lepchenko in the second round. She and Williams have never played, and both players said they know little about the other. Duan said she had never even seen Williams play. ''I don't really watch that much tennis, so I think my coach will do the job to try to tell me what I need to do on the court,'' Duan said through a translator.
No. 5 Kei Nishikori vs. Lukas Lacko: Nishikori is looking to advance to the fourth round for the sixth year in a row. He's made it to the quarterfinals the past two years. Lacko, a qualifier, has played nine sets in two rounds, including a five-setter in his first-round win over Albert Ramos-Vinolas.
Eugenie Bouchard vs. CoCo Vandeweghe: After a poor second half of 2015 and most of 2016, Bouchard is playing with more confidence. The 22-year-old Canadian, who made the semifinals here and the French Open in 2014 before reaching the final at Wimbledon, beat Vandeweghe the only time they've met at Indian Wells in 2015.