Sizzling-hot Serena Williams and top seed Agnieszka Radwanska were a pair of third-round winners Thursday at the WTA's Western & Southern Open. Venus Williams also secured a berth in the quarterfinals at this $2.168 million event.

The second-seeded Serena took care of Radwanska's younger sister Urszula, a qualifier this week, 6-4, 6-3 in 70 minutes.

The former world No. 1 Serena is currently riding a torrid 19-match winning streak since being stunned in the first round at the French Open in June. The 14-time Grand Slam champ is seeking a fourth straight tournament title after posting big wins at Wimbledon, Stanford and the London Olympic Games.

Serena's quarterfinal opponent will be quality German left-hander Angelique Kerber.

Meanwhile, the Polish world No. 3 Radwanska, who was last month's Wimbledon runner-up to Serena, outlasted American wild card Sloane Stephens 6-1, 4-6, 6-4 on the hardcourts at the Lindner Family Tennis Center.

The wild card Venus smacked seven aces in blowing past seventh-seeded Italian Sara Errani 6-3, 6-0 in 61 minutes. Errani was a surprise French Open runner- up two months ago.

Venus' opponent on Friday will be reigning U.S. Open champion Sam Stosur.

Also on Day 4 in suburban Cincinnati, the third-seeded Stosur of Australia pasted Russian Ekaterina Makarova 6-1, 6-3, while fourth-seeded Czech Petra Kvitova whipped Chinese Peng Shuai 6-2, 6-2, and fifth-seeded Kerber topped Czech qualifier Andrea Hlavackova 6-4, 7-6 (7-5). The 2011 Wimbledon champion Kvitova is fresh off her title in Montreal on Monday.

Two matches were suspended due to rain and will resume on Friday.

17th-ranked Anastasia Pavlyuchenkova won the first set of her match with sixth-seeded Caroline Wozniacki, 6-4, before it was suspended.

Sixth-seeded Li Na, who was the runner-up in Montreal last week, will also face Johanna Larsson on Friday.