ROME (AFP) - Serbian fourth seed, and defending champion, Jelena Jankovic dismantled Venus Williams' power game on Friday to advance to the semi-finals of the WTA Rome International, 5-7, 6-3, 6-2.

"I was fighting for every point," Jankovic said. "Venus is really strong, and to win you have to really play your best."

While Williams, 27, impressed with her trademark power forehand and high-percentage net play, her forehand let her down in the end, with just too many sailing over the baseline.

Jankovic raced to a 4-1 lead in the second set until Williams briefly asserted her authority with some classic serve-and-volley action.

But the American's forehand let her down again as the Serbian 23-year-old wrapped up the set 6-3.

Williams made a strong start in the third set, but the match turned for good when Jankovic broke her in the fifth game to go up 4-2. In the next game, Williams' worst, she hit three long forehands in a row.

Serving for the match, Jankovic raced to 40-0. Williams saved the first of the three match points, but the Serbian wrapped it up with a passing shot.

The world number four is to meet either ninth-seeded Patty Schnyder of Switzerland or Russian Maria Sharapova, seeded second, who were to play Friday evening.

The other semi-final will pit 18-year-old French sensation Alize Cornet -- who advanced as Venus Williams' sister Serena withdrew with a back injury -- against sixth seed Russian Anna Chakvetadze.

Chakvetadze earlier Friday but an end to a dream run for Bulgarian qualifier Tsvetana Pironkova 6-2, 3-6, 6-1.

Pironkova, 20, struggled to find the power and depth with which she upset top seed Ana Ivanovic in the second round on Wednesday.