World number one Serena Williams blew past Vania King 6-1, 6-0 and into the third round of the US but former top-ranked player Ana Ivanovic was sent crashing by a 42nd-anked Czech player.
Gusty breezes led Williams to misfire for three double faults in her first service game before the two-time defending champion found her bearings to swat aside fellow American Vania King in 56 minutes.
Ivanovic was upset 7-5, 6-4 by 42nd-ranked Karolina Pliskova in the second round.
Pliskova, 22, took advantage of a slew of miscues from the eighth-seeded Serb during an 80-minute match in Louis Armstrong Stadium to clinch her most successful grand slam appearance.
Ivanovic, 26, double-faulted seven times and committed 29 unforced errors as she had trouble handling the heavy, flat groundstrokes from the Czech.
Elsewhere, 15-year-old Cici Bellis, who shot from obscurity to fame with a shock first round win over Australian Open finalist Dominika Cibulkova, could not deliver the fairytale American tennis fans had hoped for, falling 6-3, 0-6, 6-2 to Kazakhstan's Zarina Diyas.
Third seeded Wimbledon champion Petra Kvitova booked her expected place in the third round, however, with a 6-4, 6-2 victory over fellow Czech Petra Cetkovska.