Kei Nishikori said Roger Federer was playing at his peak again following injury after he was bundled out of the Australian Open by the Swiss maestro on Sunday.
Nishikori, who went down 6-7 (4/7), 6-4, 6-1, 4-6, 6-3 to Federer in the fourth round, said he didn't see much difference in the 17-time Grand Slam winner.
"No, not really," he said, when asked if Federer had changed.
"Still playing aggressive. He was serving really well today. I don't know. I don't think it was much different. I feel like he was playing good tennis again."
Federer's ranking has dropped to 17 after he spent six months out with a knee problem, the longest injury break of his career.
The 35-year-old's chances of a first major title since 2012 are improving after the shock exit of top seeds Andy Murray and Novak Djokovic.
For fifth seed Nishikori, seeking a maiden Grand Slam win at the age of 27, it was a painful defeat in more ways than one as he twice needed treatment for an existing left hip injury.
"Physically I'm okay. Yeah, really disappointed to lose like this. Especially after I started really well," he said.
"I think I let him come back a little bit. He was playing good tennis, especially in the middle, the second and third sets. I maybe had some chances in the fifth set to come back in the match, but he was way too strong."