Wimbledon champion Elena Rybakina suffered a shock defeat by qualifier Clara Burel in the US Open first round.
Rybakina had complained about "weak leadership" on the women's tour, saying she does not feel like the Wimbledon champion because ranking points were not awarded at the All England Club.
Seeded 25th in New York, the 23-year-old was beaten 6-4 6-4 by world number 131 Burel.
Earlier on Tuesday, world number one Iga Swiatek won in straight sets.
Two-time US Open champion Naomi Osaka is out after losing 7-6 (7-5) 6-3 to American 19th seed Danielle Collins.
Poland's Swiatek, 21, needed just one hour and six minutes to beat the Italian 6-3 6-0 in New York and faces 2017 winner Sloane Stephens next.
American Stephens came back from 6-1 3-1 down to beat Belgium's Greet Minnen 1-6 6-3 6-3.
Two-time French Open winner Swiatek is one of several female players to complain about the "horrible" balls being used at Flushing Meadows.
The US Open is the only major where men and women use different balls.
Rybakina loses out ob court 12
Moscow-born Rybakina, who now represents Kazakhstan, would have moved into the world's top eight if ranking points - which were stripped because Wimbledon had banned Russian and Belarusian players - had counted.
With her ranking instead down at 25, she was scheduled on the relative obscurity of court 12 in New York.
Burel, 21, broke to go 3-2 up in the first set, before Rybakina levelled things at 4-4 but the Grand Slam winner was immediately broken again and her opponent served out the set.
The Frenchwoman was more dominant in the second set as Rybakina helped her opponent with a total of 37 unforced errors in the match.
Burel went 2-0 up and remained ahead until she claimed victory with a backhand down the line before raising her hands to the sky in relief at reaching the US Open second round for the first time.
