Second seed Simona Halep fought back from a set down to beat Sabine Lisicki and reach the quarter-final of the US Open for the first time.

Halep was troubled by a thigh problem on Louis Armstrong Stadium but, despite needing heavy strapping to her left leg, she dug deep to beat the 24th seed - who was also struggling with an injury - 6-7 (6-8) 7-5 6-2.

The outlook appeared to be bleak for Halep when she called for medical attention after the first set, but the Romanian fought on and will now face Victoria Azarenka in the last eight as she goes in search of her first grand slam title.

Lisicki will reflect on what might have been, having seemingly had Halep on the ropes when she took the first set but was ultimately made to pay for amassing as many as 72 unforced errors in a match which ebbed and flowed.

The contest was dominated by breaks of serve, with 15 coming in the first two sets and a further two in the decider seeing Halep through. 

Lisicki, aiming to reach the quarter-finals of a grand slam for only the second time, took a 2-0 lead in the first set but needed a tie-break to edge in front after saving two set points as both players struggled on serve.

The German made 30 unforced errors in the first set, with Halep making 19 in a jittery display from both players.

It was a similar story in the second set after the favourite called for medical attention. 

Eight of the first nine games in the second set went against serve before Halep levelled the match - despite needing further attention to her troublesome thigh - by breaking when Lisicki was serving for another tie-break.

There was a 10-minute break due to the searing heat ahead of the decider and it was Halep who benefited, with Lisicki, who appeared to be struggling increasingly due to injury, second best as her huge tally of errors and service issues proved to be costly.