Wimbledon winner Serena Williams and runner-up Agnieszka Radwanska along with Venus Williams were easy opening- round winners Tuesday at the U.S. Open.

The former No. 1 Serena, a three-time champ and two-time U.S. Open runner- up, had no problems in a matchup with fellow American Coco Vandeweghe 6-1, 6-1. Serena, the fourth seed, was last year's U.S. Open runner-up to Australian Sam Stosur.

In the upset of the day, eighth-seeded Dane Caroline Wozniacki was taken down by Romanian Irina-Camelia Begu, 6-2, 6-2. Wozniacki was the 2009 Open runner-up.

"You just want to go in and do your best no matter what's happening out there," said Wozniacki. "I tried and I didn't succeed today. I didn't play particularly well and made too many errors."

The second-seeded Radwanska routed Russian Nina Bratchikova 6-1, 6-1 in a mere 54 minutes at Ashe Stadium. The crafty Polish star converted on six-of-seven break-point chances in advancing against Bratchikova, who was making her U.S. Open debut.

Radwanska reached her first-ever Grand Slam final last month at Wimbledon, where she succumbed to Serena. She will meet Spaniard Carla Suarez Navarro in the round of 64, where Radwanska bowed out the last three years in Flushing.

The left-handed Angelique Kerber, seeded sixth, won her sixth match in seven tries in New York with a 6-2, 6-0 pasting of Britain's Anne Keothavong. Kerber was a surprise semifinalist here a year ago and leads the WTA in match wins this year (54-16).

Kerber will face Venus in the second round on Thursday. The German is 2-1 lifetime against the American veteran, including a win at the recently- concluded London Olympic Games.

The unseeded former world No. 1 Venus blew away fellow American Bethanie Mattek-Sands, 6-3, 6-1 at Ashe Stadium. Venus struck serves as big as 124 miles per hour on Tuesday.

"I was a little nervous in the beginning, just coming back to the Open after last year," Venus said. "It was a big deal for me. So to get back out there in front of the crowd was a wonderful feeling. But it felt great once I got on a roll and started playing some good points. Then I felt very comfortable."

Venus captured back-to-back U.S. titles in 2000 and 2001 and was the Big Apple runner-up in 1997 and 2002.

Tenth-seeded Italian Sara Errani had a little trouble with Spain's Garbine Muguruza, but overcame a second-set loss to take a 6-3, 6-7 (6-8), 6-1 victory.

Thirteenth-seeded Slovak Dominika Cibulkova overcame Swede Johanna Larsson 6-7 (5-7), 6-2, 6-0, while former world No. 1 Ana Ivanovic reached the second round with a 6-3, 6-2 handling of Ukrainian Elina Svitolina. The 12th-seeded Serb is a former French Open champ and two-time Grand Slam runner-up.

Fourteenth-seeded Russian Maria Kirilenko took an easy 6-2, 6-1 win over South African Chanelle Scheepers.

Twentieth-seeded Italian Roberta Vinci vaulted past Radwanska's younger sister Urszula, 6-1, 6-1, while 30th-seeded former No. 1 Jelena Jankovic leveled Ukrainian Kateryna Bondarenko 6-1, 6-2 on Tuesday. Jankovic was the U.S. Open runner-up in 2008.

Meanwhile,Kiki Bertens of the Netherlands defeated 21st-seeded American Christina McHale 6-4, 4-6, 6-3. American Sloane Stephens took a 6-3, 6-4 win over 22nd-seeded Francesca Schiavone, Andrea Hlavackova drove out 24th-seeded fellow Czech Klara Zakopalova 6-4, 6-4, while Japan's Ayumi Morita dismissed 26th-seeded Romanian Monica Niculescu 6-3, 6-3, and Russian Elena Vesnina knocked out 32nd-seeded Chinese Peng Shuai 7-6 (7-5), 6-1 on Day 2. Later in the day, Belarusian Olga Govortsova took down 29th-seeded Austrian Tamira Paszek 6-3, 6-4.

Also advancing at the final major of the year were Hungarian Greta Arn, Carla Suarez Navarro, Russians Vera Dushevina, Olga Puchkova and Ekaterina Makarova, Bulgarian Tsvetana Pironkova, Aussie Johanna Konta, Kazakhstan's Galina Voskoboeva and Yaroslava Shvedova, Swede Sofia Arvidsson, Spaniards Silvia Soler-Espinosa, Maria Jose Martinez Sanchez and Lara Arruabarrena-Vecino, German Tatjana Malek and Serb Bojana Jovanovski.