That 2009 triumph was one of three she achieved at Flushing Meadows, while she also won the 2011 Australian Open.
Her exploits raised the profile of tennis in Belgium, and her rivalry with Justine Henin was keenly fought, with Clijsters winning 13 of their 25 meetings -- although Henin won all three of their grand slam final matches.
Henin retired from the sport in 2011, also for the second time, and this year announced she is expecting her first child -- due to be born next March.
Clijsters said that only since retiring has she been able to see what their achievements meant to Belgian tennis fans.
"Now that I'm older I'm able to realize what we did for our country, especially in the last few months since I retired, I've been in situations where people have come up to me and thanked me," she said.
"When world leaders and politicians I've met say what you've done for Belgium, that's when it really hits you."
She was also touched that the Belgian media made a special presentation to her after that final match in September -- a second-round defeat to one of the women's game's rising stars, British 18-year-old Laura Robson.
"It's such a small country, we're very approachable. We don't have paparazzi, so we're among the people," Clijsters said.
"They said I have to come in for another interview and I thought 'Oh no, not another one.' They were all standing there ... it really got to me. The thought they put into it was very nice."
One lingering regret is that she never reached the final at Wimbledon, losing in the semis in 2006 and the quarters in 2010.
"The match that hurt me the most was that loss to Vera Zvonareva (in 2010). At the time it took me a few weeks to get myself together and focus on what was next," said Clijsters, who bounced back to win the U.S. Open for the third time later that year, beating the Russian in the final.
One of Clijsters' trademarks was her athletic stretches across the court, flexibility which could perhaps be explained by the fact her mother was a gymnast.
Clijsters, whose father was a professional footballer, enjoys the attention her quirky trademark brings.
"It does make me laugh," she said. "I have people send me pictures of splits they do to show me they can do it, so it is funny.
"I think it started because I practiced on clay all of the time in Belgium and then I just tried it one time on hard court and won the point and slowly started to feel more comfortable with it. Now more players do it, so it's not only me anymore."
So is there any chance of a third comeback? Clijsters takes her time, then shakes her head.
"No, I'm done!"