ROME — Two-time champion Jelena Jankovic rolled to a surprisingly easy 6-0, 6-1 win Thursday over Venus Williams and prevented an all-Williams semifinal at the Italian Open.

Williams struggled with her serve and never really threatened on a cool evening at the Foro Italico.

Earlier, Serena Williams overcame a rough stretch in the second set to dispatch Maria Kirilenko 6-1, 6-4.

In the other half of the draw, former No. 1 Ana Ivanovic beat 14th-seeded Nadia Petrova 6-2, 7-5 and will face 26th-ranked Maria Jose Martinez Sanchez of Spain. She defeated Lucie Safarova of the Czech Republic 7-6 (6), 6-4.

Venus returned after a month on the sideline because of right knee tendinitis. She committed 11 unforced errors to Jankovic's one in the first set. She hit two costly double-faults on one occasion to hand Jankovic a 4-1 lead in the second.

Jankovic won this clay-court warmup for the French Open in 2007 and 2008. She entered with a 5-5 career record against Venus and was not expecting an easy match.

"I had so many tough matches against Venus," Jankovic said. "It's great to win — 6-0, 6-1 is really unbelievable."

Top-ranked Serena is up next for Jankovic.

"When you play against a Williams you can't relax at all, you just have to go out there and it give it your best," the Serb said.

Serena had been out with a left knee injury since winning the Australian Open in January.

"My knee is feeling good so far," she said. "I can't believe I'm still in the tournament — it's weird."

With her ranking down to No. 58, Ivanovic recently hired Steffi Graf's old coach, Heinz Gunthardt, to improve her game.

"We've worked a lot the last few weeks and I feel great out there," she said. "I've been working a lot on the serve and I'm getting a lot of free points. My serve has been a big issue the last year and a half and having confidence in it now puts less pressure on the other parts of my game."

Since winning the 2008 French Open, Ivanovic's only title came later that year in Linz, Austria.

"I think every player goes through tough times, but it's not how many times you fall down, it's how many times you get back up," Ivanovic said. "I'm really happy to be back on track."

After cruising through the first set and taking a 4-0 lead in the second, Serena lost three straight games before regaining control on her service games. She blasted aces at 123 mph and fired baseline winners at will.

Serena had an 8-1 edge in aces and 19-7 in winners. She attributed the brief lapse to a lack of "match toughness."

"I definitely should have been up 5-0," she said. "Hopefully, as I start playing more, I'll start to close these games out better."

Serena won this tournament in 2002 en route to her only title at Roland Garros.

Martinez Sanchez maintained her focus during a brief downpour that interrupted play for 15 minutes just after the start of the first-set tiebreaker. The Spaniard also controlled the play with her big first serve, landing seven aces.