Resurgent Serena Williams [Images] overcame a strong challenge from fellow American Meghann Shaughnessy to move into the Los Angeles Open semi-finals with a 6-7, 6-1, 6-4 win on Friday.

Competing in only her third event of the year because of a knee injury, Williams dominated the last two sets in sapping heat after losing the first 7-4 on a tiebreak.

The former world number one, who had to rally from a set down to beat Slovakia's Daniela Hantuchova [Images] in the previous round, will meet Serbian Jelena Jankovic in the last four.

Sixteenth seed Jankovic upset 10th-seeded compatriot Ana Ivanovic 6-4, 7-6 in a later match, avenging her straight-sets loss in Zurich last year in the only other WTA Tour meeting between the Serbs.

In another quarter-final, third-seeded Russian Elena Dementieva recovered from a shaky first set to beat American wildcard Bethanie Mattek [Images] 4-6, 6-1, 6-1.

Despite her usual dose of double-faults, Dementieva hit form with her crunching groundstrokes to book a spot in the last four against top seed Maria Sharapova [Images] or fellow Russian Dinara Safina who were playing in the day's late match.

"I honestly should have won that first set," Williams told reporters after hitting 50 winners, including 12 aces, against Shaughnessy.

"I had a couple of chances to break and had a couple of easy shots but just let it slip away.

"But it's awesome to be in the semi-finals. I'm really feeling good about it.

MATCH TOUGH

"I'm definitely getting more match-tough, a couple of three-setters is always good to have under your belt."

Williams, whose world ranking has slipped to 110th after a truncated season, would get close to the top 50 with victory in Sunday's final.

"I feel like I'm climbing up. It's cool. I have new goals now. I'm reaching for the top 50," she added with a laugh.

Unseeded Shaughnessy, beaten in straight sets when the pair last met in the 2003 Australian Open quarter-finals, survived four break points in the opening set before coming back from 4-2 down in the tiebreak.

The 27-year-old from Scottsdale, Arizona held serve to level at 4-4 and then powered a two-fisted backhand down the line to edge ahead 5-4.

After her opponent hit a forehand long, Shaughnessy unleashed a thunderous first serve to force another Williams error and clinch the first set.

However, the twice champion then upped the tempo as court-side temperatures nudged 100 degrees.

IMPRESSIVE POWER

Generating impressive power with her groundstrokes and advancing to the net whenever possible, Williams broke Shaughnessy three times in the second set to level the match.

The deciding set went with serve until the eighth game when Williams again broke after working Shaughnessy around the court with superbly crafted rallies.

Serving for the match at 5-3, Williams was surprisingly broken for the first time after delivering her first double-fault.

Stung by her lapse, Williams took advantage of weak second serves by Shaughnessy and immediately broke back to end the encounter, her opponent double-faulting on match point.

"I started the match pretty well and it's very disappointing not to come through with that one," said Shaughnessy, the world number 77.

"I felt like I had a big letdown at the beginning of the second set. She started going more for her shots and that entirely changed the momentum of the match."

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