Williams, 27, was broken twice in the opening set, including the first game, and dropped her first set of the tournament. But after losing her serve to start the second set, she turned it on, winning six consecutive games in a dominant 29-minute second set.

Neither player was able to break in the final set but the tiebreak proved to be a battle of futility.

Jankovic started the tiebreak by missing a backhand and Williams then sent a forehand wide, but followed with a forehand approach to go up 2-1.

Jankovic would miss her next three forehands, dumping them into the net while Williams missed two of her own forehands, but ended the match with a swinging forehand volley two points later.

“I have to say well done to Venus,” Jankovic said after the match. “She played really well. She deserved to win. She was better at the end.”

Jankovic came out aggressive and sharp, breaking Williams in the evening’s first game after dropping in a topspin lob over the 12th-seed’s lanky 6-foot-1 frame.

She got another break when she ripped her trademark backhand winner down the line, blocking back Williams’ first serve to take a 4-1 lead.

Williams reeled off three of the next four games as her powerful groundstrokes began taking control but the two early breaks were too much to overcome as Jankovic took the set 6-4.

However, the second set was almost the exact opposite of the first as Jankovic was overpowered by Williams. The rallies grew shorter as Williams blasted away, running Jankovic from side to side.

Williams moves on to face top seed Justin Henin, who ousted Venus’ younger sister Serena in the quarter-finals on Tuesday night.

Earlier in the day, Svetlana Kuznetsova showed little regard for Agnes Szavy’s surprising US Open debut, storming her way into the semi-finals with a 6-1 6-4 triumph over her unseeded challenger.

Kuznetsova avoided becoming the third seeded player to fall to Szavy, the 18-year-old Hungarian who had the best women’s debut at Flushing Meadows since Venus Williams made it to the finals in 1997.

The outcome was hardly in doubt after Kuznetsova won the first three games in just nine minutes.

Szavy, who had not dropped a set in the first four rounds, committed eight unforced errors in the opening set and took far too long to recover from her sloppy start.

Szavy finally came to life midway through the second set as she bounced back from a 4-1 deficit to win the next two games and held serve to pull within 5-4.

But Kuznetsova finished the final game by winning three straight points and advanced when Szavy’s return on match point failed to clear the net.

Kuznetsova moved into the last four at Flushing Meadows for the first time since winning the title in 2004 and will face fellow Russian Anna Chakvetadze, who advanced to her first career Grand Slam semi-final with a 6-4 6-1 victory over Israeli Shahar Peer.

The sixth-seeded Chakvetadze, who lost in the quarters of the Australian and French Opens this year, seemed in danger of dropping the first set before winning 10 of the next 11 games.

The 20-year-old Russian lost her serve in the opening game of the second set but was unfazed, winning the final six.

Israeli Peer had break point in the fifth game but hit a forehand long to lose the advantage and Chakvetadze easily won the next two points to build a 4-1 cushion.

Chakvetadze wasted little time putting away the match, smashing a forehand which hit the line to capture her fifth consecutive straight-sets victory.

The sloppy second set was a disappointing end to a surprise run for the 18th-seeded Peer, who was trying to reach her first Grand Slam semi-final having lost to Kuznetsova in the quarters at the Australian Open in January.