It was an eventful first day at Flushing Meadows as Maria Sharapova made a successful return to the grand slam arena, Garbine Muguruza cruised into the second round and Johanna Konta departed.
Playing her first slam match since the 2016 Australian Open, former world number one Sharapova upstaged second seed Simona Halep in three sets on Monday.
US Open favourite and Wimbledon champion Muguruza barely raised a sweat in her first-round victory against Varvara Lepchenko.
British seventh seed Konta fell to a shock loss to Aleksandra Krunic, while fellow seeds Kiki Bertens, Ana Konjuh and Lauren Davis also said goodbye.
Seeds Caroline Wozniacki, Venus Williams, Dominika Cibulkova, Petra Kvitova, Anastasija Sevastova, Caroline Garcia, Peng Shuai, Magdalena Rybarikova, Julia Goerges and Mirjana Lucic-Baroni had no such trouble reaching the next round.
SHARAPOVA SURVIVES HALEP SHOWDOWN
The five-time grand slam champion progressed to the second round thanks to a 6-4 4-6 6-3 victory.
Sharapova walked onto Arthur Ashe for her first slam match since testing positive for a banned substance at the 2016 Australian Open, having made her return from a 15-month ban for violating anti-doping rules in April, but was denied a wildcard for the French Open and then pulled out of Wimbledon qualifying through injury.
The 30-year-old Russian star received an ovation from the crowd and delivered in an absorbing contest, lasting almost three hours as she hit 60 winners and 54 unforced errors, compared to Halep's return of 15 and 14.
KONTA FALLS AT FIRST HURDLE
Like Halep, Konta was one of eight women in contention to claim the number one ranking in New York.
However, Konta suffered a 4-6 6-4 6-3 loss to world number 78 Krunic in the opening round.
Konta only landed 45 per cent of her first serves as she departed the tournament.
MUGURUZA EASES THROUGH
The in-form Spanish star showed why she is many people's favourite for the women's singles title with a 6-0 6-3 victory over Lepchenko.
Winner of the Western & Southern Open earlier this month, Muguruza broke serve on five occasions to cruise past the world number 64.
Muguruza - who can secure the WTA's top ranking at Flushing Meadows - will next face Duan Yingying.
KVITOVA, WOZNIACKI VICTORIOUS ON DAY ONE
Two-time grand slam winner and 13th seed Kvitova progressed to the second round of the US Open for a sixth straight year after defeating Jelena Jankovic 7-5 7-5.
A quarter-finalist in 2015, Kvitova will take on Alize Cornet in the second round.
Former world number one and fifth seed Wozniacki - a runner-up in 2009 and 2014 - charged into the second round with a 6-1 7-5 win over Mihaela Buzarnescu.