Five-time champion Serena Williams and reigning titlist Agnieszka Radwanska were a pair of easy second-round winners Thursday at the Sony Open tennis event.

The world No. 1 Williams popped seven aces in whipping helpless Italian Flavia Pennetta 6-1, 6-1 in 1 hour, 17 minutes, while the fourth-seeded Radwanska rolled past Taiwan's Su-Wei Hsieh 6-3, 6-2 at Crandon Park.

The Wimbledon runner-up Radwanska beat French Open titlist Maria Sharapova in last year's Miami finale.

In addition to her five titles here, the reigning Wimbledon and U.S. Open titlist Williams is also a two-time runner-up in Miami.

Her third-round opponent will be Japan's Ayumi Morita.

Venus Williams, the event's 19th seed, downed Japan's Kimiko Date-Krumm 7-6 (7-3), 3-6, 6-4. The former world No. 1 and seven-time major champion Venus titled here back-to-back in 1998 and 1999 and was the runner-up in 2010.

Also on Day 3, fifth-seeded Australian Open runner-up Li Na whipped Dutchwoman Kiki Bertens 6-3, 6-1 and seventh-seeded former Wimbledon champ Petra Kvitova overcame Chinese Peng Shuai 5-7, 6-2, 6-2.

Ninth-seeded former world No. 1 Caroline Wozniacki came back to beat Czech Karolina Pliskova 5-7, 6-3, 6-3, while 13th-seeded Slovak Dominika Cibulkova subdued France's Kristina Mladenovic, 6-2, 6-3.

Andrea Petkovic had a 6-3, 4-1 lead over German Marion Bartoli before the 10th-seeded Bartoli retired late in the second set with a left foot injury to send Petkovic to the third round.

Romina Oprandi outlasted 17th-seeded Lucie Safarova 7-6 (7-4), 4-6 (5-7), 7-6 in a match that lasted just over 2 1/2 hours. Varvara Lepchenko, the 25th seed, defeated Romanian Irina-Camelia Begu, 6-3, 6-4 and Magdalena Rybarikova took down 27th-seeded German Mona Barthel 6-3, 7-6 (7-5).

Meanwhile, American Sloane Stephens, seeded 16th, was bageled in the first set before reaching the third round with a come-from-behind victory against Belarusian Olga Govortsova, 0-6, 6-4, 6-4.

In other action involving seeds, Spaniard Garbine Muguruza upended No. 23 Anastasia Pavlyuchenkova of Russia 4-6, 6-2, 6-2; Croat Ajla Tomljanovic took out No. 24 Julia Goerges of Germany 7-6 (7-4), 6-2; No. 30 Kirsten Flipkens of Belgium swatted Swiss Stefanie Voegele 6-4, 6-2; and the aforementioned Morita took out No. 31 Yanina Wickmayer of Belgium 7-6 (7-2), 2-6, 6-3.

The winner of this 13-day, $4.196 million tournament will earn $724,000.