Li, the No.9 seed, became China's first Premier-level champion in Sydney just over a week ago, and hasn't lost a set so far at this Australian Open, following up a 63 63 fourth round win over No.8 seed Victoria Azarenka with a 62 64 quarterfinal win over No.30 seed Petkovic. Li's forehand was particularly strong - she leads forehand winners for the tournament with 59 of them - while Petkovic's was off, as she made 15 of her 20 errors off that wing, including on match point.
"Two days ago I wanted to see how Andrea played against Maria, but Kuzy and Schiavone were playing and TV didn't show much of the other match," Li said. "It was tough. I only practiced with Andrea one time last year. So, at the beginning of the match, I was a little bit nervous. But I played well today."
This the second Grand Slam semifinal of the 28-year-old Li's career, after going this far here last year (falling to Serena Williams). Fellow Chinese Zheng Jie has also made two Grand Slam semifinals in her career, at 2008 Wimbledon (falling to Williams) and here last year (falling to Justine Henin).
Petkovic was playing in her first career Grand Slam quarterfinal.
"I think she played really well. I think she's going to win the tournament," Petkovic said. "It's just the feeling, how she is on the court, her confidence and the way she's playing. I feel she has a great chance to win the tournament.
"Sometimes you get the feeling during the match that somebody is really strong and just has that confidence going on, that aura maybe."
Next up for Li will be either No.1 seed Caroline Wozniacki or No.6 seed Francesca Schiavone, who played later in the afternoon on Rod Laver Arena.