Williams has a 7-1 record against semi-final opponent Henin

Williams dropped the first set but looked to have complete control of the match when she won six games in a row to take it into a third set.

But Jankovic came back at Williams and twice had break points in the decider.

However, it went to a tiebreak and the twice former champion's experience proved the difference.

"I would have loved to have a couple breaks in the third set and cruised," said Williams.

"She's a very good competitor, and anyone has to play a lot of balls against her. I just went for it all the time non-stop and it paid off."

Venus now plays Justine Henin, who beat Serena in the last eight, and she added: "I have to win for Williams."

Wimbledon champion Williams unleashed 60 winners but made 57 unforced errors in a patchy performance - partly affected by some bold baseline play from her opponent.

But Jankovic made a series of errors when it mattered most in the third-set tiebreak.

The Serb clawed back from 5-1 to 6-4 but Williams sealed it with a forehand winner.

"Well done to Venus," said Jankovic. "She played unbelievable. She fought well. She deserved to win."