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The Swiss, seeded second, won 7-5 6-4 5-7 6-3 to set up a meeting with Juan Carlos Ferrero in the last four.

Nalbandian came into the match having not dropped a set, but in a tight match it was Federer who won the vital points.

He edged the first two sets and, after dropping the third, claimed an early break in the fourth and held on.

Federer said the big serves he produced at crucial moments had won him the match.

"I took a lot of chances. The aces came at the right time and that was maybe the key to the match," Federer said.

Nalbandian added: "I can't say I played bad. I think the match was very, very close. I think on the important points, the big points he played better than me. That's the difference."

Nalbandian had a 5-1 record against Federer before the match, but the Swiss won their last encounter with ease at the Masters Cup in November.

And his increased confidence was evident in the decisive moments.

With the score at 6-5 and 30-30 in the opening set he played a patient point that ended with a move to the net and a sharp volley.

Nalbandian then gave up the break with a poor forehand, and that proved to be the story of the match.

The Argentine twice broke to go ahead in the second set but from 4-3 down Federer stormed back to take a decisive two-set lead.

There were more break-point opportunities for Nalbandian in the third set but it took until the 11th game for him to convert and haul himself back into the match.

A real comeback from the eighth seed was not on the cards, however and, after breaking at the first opportunity, Federer served out the fourth set and the match.