MELBOURNE -- Roger Federer showed his full-on championship form but Stan Wawrinka was felled by a post-surgery knee as the Swiss former Australian Open champions split the difference in the second round on Thursday.
The pair got lucky from a weather standpoint, playing cooler (88-degree) night matches after 104-degree summer daytime temperatures.
Federer, in the hunt for a sixth Melbourne title and 20th Grand Slam singles title, won 6-4, 6-4, 7-6 (7-4) against German Jan-Lennard Struff.
But 2014 Melbourne winner Wawrinka showed that he still needs more recovery time after his summer knee operation, falling to American Tennys Sandgren 6-2, 6-1, 6-4 in 88 minutes with 35 unforced errors.
"I was struggling with everything, not the knee especially, the knee was still handling well," said Wawrinka, a three-time Grand Slam winner.
"As long as I enter on the court, and I don't feel any big injury, I'm not going to retire (from a match). I was here to fight and to try everything I could."
Federer played and won his 102nd Australian Open match and is one of two men -- Jimmy Connors is the other -- to have played at least 100 matches at any Grand Slam event.
Federer's only wobble came as he went down a break in the third set, getting it back for 3-all with a clean passing winner.
But he did have to clinch it in a tiebreaker, firing a service winner to close out victory.
"I've trained with him and played him so I had the information on his game," Federer said. "I knew he would go for his shots.