Ana Ivanovic's frustrating run continued on Monday as she became the first major casualty of the US Open.
Since her semi-final appearance at the French Open, the world number seven has only won five matches on the WTA Tour, and Monday's defeat at the hands of Dominika Cibulkova is another major disappointment.
Her first-round exit is the second of 2015 after suffering the same fate at the Australian Open, while she was beaten in round two at Wimbledon.
The seventh seed made a confident start at Flushing Meadows but she failed to capitalise on a break in the fifth game as she promptly lost four successive games to give Cibulkova the set.
Ivanovic bounced back in the second, though, and came from 3-1 down to win five in a row to level the match at 6-3.
She failed to use that momentum though as she was broken twice at the start of the decider, Cibulkova – who had fallen at the first round at the last two US Open tournaments – showing her fight to cruise through.
There was a brief glimmer for the Serb in the seventh game but Cibulkova – who reached the Australian Open final this year – held her nerve and booked a second round place.
US Open results on Monday, the first day of the 2015 tournament at Flushing Meadows:
Bethanie Mattek-Sands (USA) bt Kateryna Kozlova (UKR) 6-4, 6-3
Magda Linette (POL) bt Urszula Radwanska (POL) 7-6 (7/3), 6-1
Agnieszka Radwanska (POL x15) bt Katerina Siniakova (CZE) 6-2, 6-3
Irina Falconi (USA) bt Samantha Crawford (USA) 6-4, 6-2
Venus Williams (USA x23) bt M?nica Puig (PUR) 6-4, 6-7 (7/9), 6-3
Anastasia Pavlyuchenkova (RUS x31) bt Magdaléna Ryb?rikov? (SVK) 6-4, 7-5
Anett Kontaveit (EST) bt Casey Dellacqua (AUS) 7-5, 6-2
Madison Brengle (USA) bt Zheng Saisai (CHN) 6-2, 5-7, 7-5
Anna Tatishvili (USA) bt Karol?na Pl?skov? (CZE x8) 6-2, 6-1
Bojana Jovanovski (SRB) bt Lara Arruabarrena (ESP) 6-2, 6-2
Kristina Mladenovic (FRA) bt Svetlana Kuznetsova (RUS x30) 6-3, 7-5
Elina Svitolina (UKR x17) bt Elizaveta Kulichkova (RUS) 6-1, 6-4
Kaia Kanepi (EST) bt Anna-Lena Friedsam (GER) 6-1, 6-1
Lauren Davis (USA) bt Heather Watson (GBR) 7-6 (7/3), 7-6 (7/0)
Ekaterina Makarova (RUS x13) bt Teliana Pereira (BRA) 6-3, 6-3
Denisa Allertova (CZE) bt Carla Su?rez (ESP x10) 6-1, 7-6 (7/5)
Mariana Duque (COL) bt Sofia Kenin (USA) 6-3, 6-1
Océane Dodin (FRA) bt Jelena Jankovic (SRB x21) 2-6, 7-5, 6-3
Polona Hercog (SLO) bt Zarina Diyas (KAZ) 6-2, 7-5
Jessica Pegula (USA) bt Alison Van Uytvanck (BEL) 7-5, 6-3
Dominika Cibulkova (SVK) bt Ana Ivanovic (SRB x7) 6-3, 3-6, 6-3