World number one Serena Williams will meet defending champion Elena Dementieva in the final of the Sydney International.

World number one Serena Williams will meet defending champion Elena Dementieva in the final of the Sydney International after the pair advanced in contrasting fashion today.

Williams survived a massive scare before going through with a 3-6 7-5 6-4 win over Aravane Rezai while Russian Dementieva had a convincing win over Victoria Azarenka of Belarus 6-3 6-1.

After dropping just seven games in her previous two matches, Williams struggled on serve early as Rezai had all the early break-point chances in the first set before eventually converting her sixth opportunity in the seventh game.

The world number 27 broke again at 5-3 to seal the first set and carried that momentum into the second where she gained an early break to move out to a 4-1 lead.

But the Frenchwoman got the jitters when serving for the match at 5-3 and a double fault at 30-30 handed Williams her first break-point opportunity, which she duly converted.

The American broke again, winning five games in a row to take the second set and force a decider.

The pair traded breaks twice in the final set before Williams was finally able to consolidate and close out the match in just over two hours.

"I was lucky to get through today, for sure," Williams said.

"I was trying to play my game and do the best that I could but I didn't do so well. I hit I don't know how many errors today, but I finally made a couple of shots."

In the other semi-final, fifth seed Dementieva produced a dominant performance over sixth-seeded Azarenka that lasted just over an hour.

Both women had trouble holding serve in the opening set, but it was Dementieva who made the most of her opportunities, converting four break points to two and taking the set in quick time.

While Azarenka had the better of the first serve percentage for the match (80 to 64), the 20-year-old struggled to find an answer to Dementieva's impressive ground strokes and as the game wore on the Russian asserted her authority over her younger opponent.

The second set quickly ran away from the world number seven as unforced errors began to creep into her game, while Dementieva was ruthless on Azarenka's serve, converting both break-point opportunities to wrap up the match.

In the men's draw, fourth seed Lleyton Hewitt lost his quarter-final with Marcos Baghdatis.

After claiming the opening set in a little less than an hour, the Australian looked on target for an easy victory early in the second before the world 42 took command.

Hewitt's wayward serve and a string of unforced errors allowed Baghdatis back into the contest, and the popular Cypriot took full advantage by winning six consecutive games to extend the match.

Having claimed the early break in the final set, Baghdatis showed glimpses of the form that saw him progress to the 2006 Australian Open Final, mixing power and precision to comfortably progress to the last four.

In the top half of the draw, Richard Gasquet and Julien Benneteau won their respective quarter-final matches and will now meet in an all-French semi-final.

Gasquet defeated Italian Potito Starace 6-3 7-6 (9-7) while Benneteau needed more than two hours to overcome Argentinian qualifier Leonardo Mayer 6-4 6-7 (5-7) 6-0.

Baghdatis will play American Mardy Fish, who beat Australia's Peter Luczak 7-6 (7/5) 6-2, in the last four.