Top seed Jelena Jankovic battled to an impressive 7-5, 6-4 win over Nadia Petrova to reach the semi-finals of the Los Angeles Classic on Friday.
Jankovic, who is closing in on the world No.1 ranking, will face Dinara Safina in the last four after the Russian crushed Victoria Azarenka 6-3, 6-1.
Italy's Flavia Pennetta reached her first WTA Tour second tier semi-final with a 7-6, 3-6, 6-1 victory over 14th seed Sybille Bammer of Austria. She will face unseeded American Bethanie Mattek, who beat China's Yuan Meng 6-2, 7-5.
Jankovic came back from breaks down in both sets to defeat Petrova, who missed an easy forehand volley to lose the first and then tossed her racket angrily into her chair.
The Russian let a 3-1 lead slip in the second and was broken to lose the match when she erred on a forehand approach shot.
"She's really improved over the past year," Petrova said.
"She's not just running on the baseline anymore, she's serving better and taking the ball earlier and coming forward."
'HUNG IN THERE'
Jankovic, who came into the tournament nursing a knee injury, said her leg is holding up well and her movement has improved with each match.
"I played the big points well and was able to come back," the Serbian said.
"I did quite well when it was the important times. I hung in there and hit my shots when I needed to."
Safina, who needed more than two and half hours to beat fellow Russian Alla Kudryavtseva on Thursday, looked sharp on a hot afternoon against Azarenka.
"Sometimes you need those kind of matches where it's good, bad, you are fighting, it puts everything out of you," the fourth-seeded Safina told reporters.
"It was a perfect match," said Safina, who is seeking her first title on US soil. "I have nothing bad to say. My coach said it was the best match I ever played."