No.1 seed Caroline Wozniacki got off to a perfect start at the US Open, defeating American Chelsey Gullickson in straight sets.
The Dane easily accounted for the local wildcard 6-1 6-1 in an hour.
Gullickson hit 30 unforced errors in the match, and typified her performance by hitting into the net on match point, with her inexperience allowing Wozniacki an easy victory.
China's Li Na was the highest seed to fall on Day 2 at Flushing Meadows in the women's singles, falling to Ukraine's Kateryna Bondarenko in three sets.
The world No.59 ran over the eighth seed in the final two sets, winning 2-6 6-4 6-2.
Andrea Petkovic was also a giant-killer, knocking out Russia's Nadia Petrova.
The 38th-ranked German beat the 17th seed in a third-set tiebreaker, winning 6-2 4-6 7-6 (7-4).
Russian seventh seed Vera Zvonareva had little trouble accounting for Slovakia's Zuzana Kucova 6-2 6-1.
Earlier in the day, 11th seed Svetlana Kuznetsova defeated 40-year-old Kimiko Date Krumm in three sets 6-2 4-6 6-1.
Maria Jose Martinez Sanchez also required three sets to beat American Jamie Hamption 6-4 3-6 6-0.
Australian Alicia Molik fell in her first round encounter against Mirjana Lucic, going down 7-6 (7-5) 6-1.
Germany's Sabine Lisicki thrashed local Coco Vandeweghe 6-1 6-0, allowing the American just 20 points for the match.
Russian and 23rd seed Maria Kirilenko toughed out a straight-sets win over former junior world No.1 Barbora Zahlavova Strycova 7-5 6-4.
World No.371 Beatrice Capra won her first main draw singles match at a Grand Slam by defeating Karolina Sprem in emphatic fashion 6-1 6-3.
The American teenager, who is listed as an amateur, will play 18th seed Aravane Rezai in the second round, after the Frenchwoman beat Magdalena Rybarikova 7-6 (7-5) 7-6 (9-7).
Pole Urszula Radwanska beat Anna Chakvetadze in straight sets 6-3 6-3.
Radwanska's sister and ninth seed Agnieszka also won through to the second round, defeating Arantxa Parra Santonja 6-4 6-3.
China's Peng Shuai came from a set down to beat America's Shelby Rogers 6-7 (5-7) 7-6 (7-3) 6-3.
Bethanie Mattek-Sands gave the local fans something to cheer about with a three-set win over Anabel Medina Garrigues 4-6 6-4 6-1.
However, Yvonne Meusburger was not reading the same script of allowing Americans through to the second round, as she beat Jill Craybas 3-6 7-5 6-0.
Meusburger's compatriot Tamira Paszek caused an upset when she beat 26th seed Lucie Safarova 2-6 7-5 6-2.
Swiss Patty Schnyder smashed Kirsten Flipkens 6-1 6-3, while Julia Georges defeated Romina Oprandi 6-3 6-4.
World No.84 Kai-Chen Chang defeated the more-fancied Carla Suarez Navarro of Spain 6-2 6-4.
Belgian 15th seed Yanina Wickmayer smashed Alla Kudryavtseva 6-1 6-2.
Kaia Kanepi flew the Estonian flag on Tuesday, as the 31st seed beat Alize Cornet after a slow start 3-6 6-1 6-0.
Swede Sofia Arvidsson beat Romanian Sorana Cirstea 6-1 6-2, while Yung-Jan Chan blew away Briton Anne Keothavong after a slip-up in the opening set, running out a 2-6 6-1 6-1 winner.
Uzbekistan's Akgul Amanmuradova beat South African Chanelle Scheepers 6-3 6-4, while 25th seed Romanian Alexandra Dulgheru beat Julie Coin 6-3 6-1.
Iveta Benesova beat Nuria Llagostera Vives in straight sets, but Lourdes Dominguez Lino produced an upset overcoming 30th seed Yaroslava Shvedova in three sets.
Anastasija Sevastova kept Regina Kulikova game-less in their match before the Russian retired at 6-0 2-0, and Dominika Cibulkova struggled past Stefanie Voegele in a tight three-setter.