Victoria Azarenka has admitted that she was "surprised" by how much pace Simona Halep got on the ball during their quarter-final match at the US Open on Wednesday.

The two-time finalist at Flushing Meadows managed to fight back from a set down to send the clash into a third set, but a rain delay halted the Belarusian's progress.

Eventually, Halep, who has never before reached the semi-finals in New York, secured a 6-3 4-6 6-4 victory.

"I think I played well," Azarenka told reporters after the match. "I believe I could have played better. I did really fight really hard, and I was trying to find solutions.

"She played really well today. I was a little bit surprised by the pace of her ball to be honest. I think that, you know, a couple of free points that I gave away today cost me the match a little bit."

Halep will take on Flavia Pennetta in the semi-finals.