India's Sania Mirza advanced to the second round of the Cincinnati Open after her opponent retired due to injury.
Sania was leading 6-1, 2-0 when Alexandra Stevenson of the US retired with a right shoulder strain. She will take on world number 66 Emma Laine of Finland in the next round.
The Indian ace had earlier reached the second round of doubles with Marta Domachowska of Poland with a comfortable 6-4, 6-3 victory over Natalie Grandin and Milagros Sequera.
Former world number one Serena Williams made a spectacular return to action on Tuesday sweeping past second seed Anastasia Myskina of Russia 6-2, 6-2 in the first round.
Sidelined with an injured left knee since the Australian Open, Williams showed few signs of rust or nerves, disposing of the 2004 French Open champion in just 56 minutes at the season- opening hard court event.
After missing the French Open and Wimbledon, Williams has an eye on the US Open and underlined her hard court credentials with a ruthless display against the world number 11.
Out of action since the third round of the Australian Open, the muscular Williams broke Myskina at the first opportunity on the way to claiming the opening set.
"I think there's definitely some rust there still but I think mentally I did better than I thought I was going to do," Williams told reporters.
Despite her prolonged absence, Williams had few lapses in concentration and was clearly enjoying being back in the tennis spotlight.
"What I missed most was the competition," said the seven-time Grand Slam winner, who has now won all four career meetings with Myskina.
"I've always said, I love to win whether it's a match or a tournament. I love winning. I think I missed that a lot."
Myskina was the only seed to be shown the exit on a busy day of action.
Fourth-seeded Katarina Srebotnik of Slovenia advanced with a 6-3, 7-6 (7-3) win over Paraguay's Rossana De Los Rios while fifth-seeded Serbian Jelena Jankovic eased into the second round with 6-3, 6-2 win over Ukrainian Olga Savchuk.
Sixth-seed Frenchwoman Marion Bartoli cruised past Taiwan's Chin-Wei Chan 6-2, 6-3 while eighth-seeded Gisela Dulko of Argentina defeated Poland's Marta Domachowska 7-5, 6-3.
