American teenager Coco Gauff's hopes of another dream Grand Slam run were ended in the US Open first round after a lacklustre performance in a defeat by 31st seed Anastasija Sevastova.
A second-set resurgence looked to put Gauff, 16, on track for victory against the Latvian but she lost 6-3 5-7 6-4.
World number 51 Gauff reached the third round at her home Grand Slam in 2019, soon after making Wimbledon's last 16.
Meanwhile, top seed Karolina Pliskova and sixth seed Petra Kvitova advanced.
Gauff, who had backed up last year's promise by reaching the fourth round at January's Australian Open, could not reproduce that form against a relentless Sevastova, 30.
The Latvian - a semi-finalist in 2018 - overcame her frustration at narrowly losing the second set after the pair continually exchanged breaks. She surged ahead at 5-4 up in the third to break Gauff's serve and claim victory.
Gauff was let down by a huge 12 double faults and went out when she netted a return to make her first opening-round exit from a Grand Slam tournament.
Confident starts for top seeds
Pliskova made a confident start to her campaign in New York with a 6-4 6-0 win over Ukraine's Anhelina Kalinina.
The 28-year-old Czech, who is top-ranked in the absence of Ashleigh Barty and Simona Halep, faces France's Caroline Garcia next.
Former Wimbledon champion Angelique Kerber, playing her first match since January's Australian Open, beat Australian Ajla Tomljanovic 6-4 6-4.
Czech sixth seed Kvitova overcame Romanian Irina-Camelia Begu 6-3 6-2, hitting 23 winners in an assured performance.
Japan's 2018 champion Naomi Osaka will be in action around 02:00 BST on Tuesday.
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