Defending champion Angelique Kerber was knocked out in round one of the US Open by Japanese teenager Naomi Osaka.
The German sixth seed was overpowered by the 19-year-old world number 45, who won 6-3 6-1 under the roof on Arthur Ashe Stadium at Flushing Meadows.
It continues a disappointing year for 29-year-old Kerber, who has not won a title since her victory in New York 12 months ago.
She was also beaten in the first round of the French Open.
Osaka, who led Madison Keys 5-1 in the final set in round three of last year's US Open before losing, said: "It means a lot, especially since last time I was here.
"This court has not given me fond memories but hopefully this overtakes that. "When it was 4-1 today I was thinking, 'I really hope I don't do what I did last year' and that let me focus a lot."
Two-time Grand Slam champion Kerber struggled badly with her second serve, winning only 37% of points behind it. Osaka hit 22 winners to Kerber's nine, while the German also made 23 unforced errors in a erratic display.