Ana Ivanovic was one of the first winners on the Day 2 schedule, beating Anna Tatishvili, 62 60.
Elena Vesnina also cruised in her first round match, out-hitting Annika Beck in straights, 61 61.
Duan Ying-Ying made an impression in her Grand Slam debut, pushing Caroline Wozniacki to the limit.
But Wozniacki showed her mettle, rallying from 5-2 down in the second set to advance, 62 75.
Golf star Rory McIlroy was in the stands watching good friend Wozniacki battle until the end.
Ivanovic met Philadelphia Phillies baseball stars Kevin Frandsen, Michael Young and John McDonald.
Elina Svitolina pulled off one of the big upset of the day, defeating No.17 seed Dominika Cibulkova.
Heather Watson came close to an upset but succumbed to red-hot No.21 seed Simona Halep, 46 64 62.
But the biggest surprise of the day came later, as a No.296-ranked American qualifier stepped up...
In her first match against a Top 20 player, Victoria Duval stunned No.11 seed Sam Stosur, 57 64 64.
Victoria Azarenka had no trouble in her opener, though, cruising on Arthur Ashe Stadium at night.
Azarenka outclassed Dinah Pfizenmaier, 60 60, though the German did have 11 game points in the match.