ROME (Reuters) - Venus Williams will face Samantha Stosur when she returns this week after more than a month out of action after the Australian beat Michaella Krajicek 6-3 6-2 on Monday to set up a second-round encounter at the Italian Open.

The American six-times grand slam champion, seeded seventh for this tournament, has been sidelined with an unspecified medical problem.

Fifth seed Serena Williams, who like her sister Venus is a former Italian Open champion, will start her campaign against Alona Bondarenko after the Ukrainian blew away Italian wildcard Mara Santangelo 6-2 6-2 in the first round.

Russian 10th seed Vera Zvonareva stayed on course to meet Venus Williams in the third round by beating Japan's Ai Sugiyama 6-3 6-3.

Zvonareva lost her serve four times in the match but was able to break the Japanese player almost at will to ease through.

Zvonareva's compatriot Dinara Safina, who won the German Open on Sunday and was defeated in the Rome final by Martina Hingis in 2006, has pulled out of the tournament with a back injury, organisers said. Her place has gone to Austria's Sybille Bammer.

Third seed Svetlana Kuznetsova, another Russian, will meet Belarusian Olga Govortsova, who rallied to beat Italy's Karin Knapp 4-6 6-1 6-2.

Hungarian 11th seed Agnes Szavay made light work of China's Yan Zi, triumphing 6-1 6-1.

Top Italian Francesca Schiavone had to battle harder to overcome Czech Lucie Safarova 6-4 7-5 in a match in which over half of the games went against serve.

Russian world number two Maria Sharapova and top seed Ana Ivanovic have byes to the second round, along with the Williams sisters and the other highest seeds.

Serbia's Ivanovic was in upbeat mood on Monday, saying she has improved massively since winning the German Open a year ago.

"I have matured a lot on court," she told a news conference. "I feel I'm playing more consistently and I've had lots of wins over top players, which for sure gives me confidence.

"This is the best time of my career so far, the highest I have been ranked and the best tennis I have played. I just want to keep the hard work up and the results and hopefully make one more step at a grand slam and win a title."

(Reporting by Paul Virgo, editing by Miles Evans)