"It's the place that has inspired me so much to do well and to do great things. It's hard to explain sometimes why," Clijsters said in an on-court interview, her face flushed and her eyes welling with tears.
"This completely feels like the perfect place to retire," she told the spectators at Arthur Ashe Stadium, many of whom rose to shower her with a standing ovation. "I just wish it wasn't today."
Her previous defeat at Flushing Meadows came against Belgian rival Justine Henin on Sept. 6, 2003, in the tournament final. Robson was 9 at the time.
This did have the feel, in some ways, of a changing of the guard.
Clijsters finished with a career singles record of 523-127 (a winning percentage of .805) and 41 titles, including her last major trophy at the 2011 Australian Open. She spent a total of 20 weeks ranked No. 1, as recently as February 2011.
Ranked 89th, and with only one prior victory over a top-25 player, Robson has been viewed - particularly back home in Britain - as an up-and-coming player whose smooth left-handed strokes would carry her far.
But she had never produced the kind of grit and court-covering athleticism that carried her past the 23rd-seeded Clijsters. And until now, Robson never had won more than one match in a Grand Slam tournament; her claim to fame had been teaming for a silver medal in mixed doubles at the London Olympics with Andy Murray, who played his second-round U.S. Open match Wednesday night.
Robson knows, though, how much Clijsters means to the game, not only as a superb player but as someone who by all accounts is universally liked - by fans, tennis officials and even opponents.
"She's always been someone that I've looked up to since I started on the tour. She's always been incredibly nice to be around," Robson said. "I think we're all going to miss her."
When the contest ended with Clijsters sailing a backhand return long, allowing Robson to convert her third match point, they met at the net. Clijsters began to extend her arm for the customary handshake, and Robson pulled her in for a hug.
"I want to thank Kim," Robson told the crowd, "for being such a great role model to me for so many years."
Clijsters was the only seeded woman who lost during the afternoon session of Day 3, when the winners included No. 1 Victoria Azarenka, defending champion Sam Stosur, 2011 Wimbledon champion Petra Kvitova and 2011 French Open champion Li Na.
Joining Robson with a surprise victory was American wild-card entry Mallory Burdette, the NCAA runner-up who reached the third round in her Grand Slam debut by eliminating 69th-ranked Lucie Hradecka, 6-2, 6-4.
In the evening, third-seeded Maria Sharapova needed just 54 minutes to advance, beating Lourdes Dominguez Lino, 6-0, 6-1. Defending champion Samantha Stosur claimed a 6-3, 6-0, second-round victory over Edina Gallovits-Hall of Romania.
Earlier on Ashe, the highest-ranked American man, John Isner, let out a big exhale of relief while waving to the crowd after getting past an argumentative Xavier Malisse, 6-3, 7-6 (5), 5-7, 7-6 (9), in the first round.
"I know in the nitty-gritty times of a match, I always have that confidence and all those wins in my back pocket," said Isner, who is 37-13 in tiebreakers this season.
No. 3 Andy Murray reached the third round for the seventh year in a row, beating 118th-ranked Ivan Dodig of Croatia, 6-2, 6-1, 6-3.