Agnieszka Radwanska admitted her 13-match winning streak to start 2013 could have taken a toll as she exited the Australian Open on Tuesday.
Radwanska had not dropped a set, let alone a match, entering her quarter-final against Li Na but found the going tough as the Chinese sixth seed won 7-5 6-3 to advance to her third semi-final at Melbourne Park.
Li, runner-up two years ago, took the opening set in 66 minutes before racing to a 5-2 lead in the second.
The Pole then held to force Li to serve it out and, despite trailing 15-40, she reeled off four consecutive points to secure victory when Radwanska pushed a backhand long.
"Some of the games she didn't let me do anything - very deep balls all the time, good serve, she was really playing good tennis today," Radwanska said.
"I think she's a very consistent player. She's always playing on the same level. It's not up and down like the other girls. She's always playing solid tennis.
"Of course, I had my chances but, when you're not really taking them, it's really turning around and it goes away."
Radwanska, 23, went into the first grand slam of the year having won titles in Auckland and Sydney in the lead-up.
And she conceded she was starting to feel the wear and tear of a lengthy campaign so far.
"Of course I could feel I was playing already a lot of matches. But playing every second day helps a little bit that I could rest between the matches," she said.
"But definitely I think I wasn't fast enough today. Especially from the beginning of the match, I was really running a lot. It cost me a little too much power in the beginning of the match."
Radwanska said she would return home to Poland for a few days to recharge the batteries before preparing for the Fed Cup in early February.
Radwanska and Li had met nine times before with the Chinese player extending their head-to-head record to 6-4.