Samantha Stosur returns a shot against Kristina Mladenovic at the Washington Open on Tuesday. Photo: IC

Australia's Samantha Stosur, the 2011 US Open champion, won her 500th career singles match victory on ­Tuesday, defeating France's Kristina Mladenovic 6-2, 6-2 at the WTA and ATP Washington Open.

The 31-year-old second seed from Brisbane needed only 64 minutes to improve to 4-0 against Mladenovic and book a second-round date with American Irina Falconi.

"My serve set me up. There weren't a lot of long rallies. Bing. Bang. It was over," said Stosur, who had no clue about the landmark win total until well after the victory.

"Now that I know, [feels] really good," Stosur said of her milestone ­triumph.

The top Aussie on the all-time women's match win list is Evonne Goolagong Cawley with 695.

In pondering her all-time top ­triumphs, Stosur went directly to her Grand Slam title run, which she won by defeating current world No.1 and 21-time Grand Slam champion ­Serena Williams 6-2, 6-3 in the final four years ago at Flushing Meadows.

But also drawing her attention was a three-set US Open semifinal win over Germany's Angelique Kerber, a three-set thriller over Russian Maria Kirilenko in the round of 16 and a third-rounder over Nadia Petrova she took 7-5 in the third after splitting two tiebreakers.

"Obviously the US Open has been the highlight, not just the final - a ­couple matches in there were really tight," Stosur said. "And maybe the first time I won a final back in Osaka.

That Osaka title came in 2009 with a finals win over Italy's Francesca ­Schiavone and after Stosur had recovered from Lyme disease, which sidelined her for parts of the 2007 and 2008 campaigns.

"A few matches I lost have been memorable," she said. "There have been a lot of great moments. I've had those highs along the way and lows as well."

Stosur, ranked 21st, is coming off her second title of the year, and the eighth of her career, on the Austrian clay at Bad Gastein.

She also won on clay at Strasbourg in May but makes her first visit to the US capital event to start her US Open preparations.

"I'm feeling good," ­Stosur said. "It's nice to get back on the hard courts again."