Ljubicic is the playing captain of the Croatian Davis Cup team

The Argentine made the number six seed work hard for the first set, forcing a tie-breaker which Ljubicic took 7-4.

But he was no match for Ljubicic in the second, which the Croatian won comfortably to go through 7-6 6-3.

Ljubicic's Davis Cup team-mate Mario Ancic was not able to match his feat, however, as the 22nd seed lost 6-2 6-2 to third seed David Nalbandian.

The Argentine eliminated Ancic in 56 minutes, hitting 21 winners with only nine unforced errors.

I feel like the number two player in the world Ivan Ljubicic

"I played almost perfect from the beginning until the end," Nalbandian said. "So I'm very happy."

He will now play the in-form Ljubicic in Friday's semi-finals.

Ljubicic has won 24 of his 27 matches on the men's tour this season, second only to world number one Roger Federer who he could meet in Sunday's final.

"Definitely I feel like the number two player in the world," said Ljubicic. "It's not just a feeling. I think the numbers are showing the same."

Federer, the defending champion, plays American James Blake on Thursday for a semi-final berth.

Fourth seed Andy Roddick, the 2004 champion and another home favourite, faces Spain's David Ferrer in the other quarter-final.