Kei Nishikori believes fatigue and pressure got to him in his straight-sets quarter-final loss to Stan Wawrinka at the Australian Open on Wednesday.
The Japanese fifth seed was well-beaten at Rod Laver Arena, going down 6-3 6-4 7-6 (8-6) to defending champion Wawrinka in Melbourne.
Nishikori paid tribute to Wawrinka for his performance, but said he had felt "heavy" during the encounter.
"For me, no, not really [any nerves]," he told a media conference.
"I felt little bit tired, heavy. But, I mean, mentally I was fine and I was ready to go. But he was little better today."
Wawrinka gave up just 15 points when serving in the first two sets as Nishikori struggled to make inroads returning.
Nishikori said a poor start was costly, while Wawrinka's aggression made it difficult for him to settle into the match.
"For sure, I didn't start well," he said.
"First couple games I was missing so much, so many unforced errors. I was going for too much.
"I don't know. I maybe felt a little bit of pressure.
"But he was serving really well today because I usually return well and break a couple games.
"So it was tough to find my game today and he was playing really aggressive, great forehand, backhand. So, yeah, I thought he was playing great."