Australian second seed Samantha Stosur has advanced to the semi-finals of the Washington Open, when opponent Romania’s Monica Niculescu retired less than half an hour into their match.

The 2011 US Open champion was leading 4-0 in the first set when her opponent abandoned the game with a left abdominal strain.

“It seemed like straight away, something wasn’t right with her,” said Stosur, adding that while she never wants to take advantage of an opponent’s injury, she was “not going to complain” about advancing with less than a half-hour of time on court.

Stosur will face Sloane Stephens for a berth in the women’s final. Stephens advanced with a 6-4 6-4 victory over 19-year-old wild-card entry Louisa Chirico.