By Chris Oddo

(March 21, 2013) -- Serena Williams made light work of former top ten player Flavia Pennetta on Thursday morning during second round play at the Sony Ericsson Open in Miami.

The six-time champion hit seven aces and saved all seven break points she faced in the 6-1, 6-1 victory, which sets up a third-round clash with Japan's Ayumi Morita.

Read: Sony Open WTA Draw Preview

Making her first appearance since pulling out of Dubai in February with a back injury, Williams increased her career record against Pennetta to 4-0, breaking serve five times out of 18 break point opportunities.

It was a good day for all top seeds in Miami, as Agnieszka Radwanska, Li Na and Petra Kvitova all moved into the third round.

Radwanska, the defending Miami champion, took care of Su-Wei Hsieh, 6-3, 6-2. The fourth seed, who defeated Maria Sharapova in last year's final, has never successfully defended any of her 12 career titles. “That's why I'm here,” the 24-year-old said afterwards. “I will do anything to hold the trophy again.”

Fifth-seeded Li Na, playing her first competitive tennis since the Australian Open, raced past Kiki Bertens of the Netherlands, 6-3, 6-1. Li will face either Varvara Lepchenko or Irina-Camelia Begu in the third round. The 31-year-old saved both break points she faced in her first meeting against Bertens.

Seventh-seeded Petra Kvitova dropped the first set to China's Peng Shuai but rebounded to defeat the World No. 34 for the third time in three career matches, 5-7, 6-2, 6-2. Kvitova has never been past the third round at the Sony Open in five career appearances. Last year she bowed out to Venus Williams in three sets in the second round.

In other second round action, Sloane Stephens turned things around after a horrible start to defeat World No. 64 Olga Govortsova, 0-6, 6-4, 6-4. “I was asleep out there,” Stephens told reporters after she was done. “I definitely just needed to wake up and start playing.”

Stephens awaits the winner of tonight's Venus Williams-Kimiko Date-Krumm match in the third round.

19-year-old wildcard Ajla Tomjlanovic notched another surprise victory when she took out 24th-seeded Julia Goerges, 7-6(4), 6-2. The World No. 242, who trains at the Evert Academy, will face Andrea Petkovic, who advanced when Marion Bartoli was forced to retire with an injury in the second set.

Spanish Wildcard Garbine Mugurazu also notched an upset when she defeated 23rd-seeded Anastasia Pavlyuchenkova, 4-6, 6-2, 6-2.

Also advancing in second-round action were 9th-seeded Caroline Wozniacki and 13th-seeded Dominika Cibulkova.

(Photo Credit: Melissa DeJong)