Halep outlasts Azarenka to reach maiden semi

Simona Halep is through to her first US Open semi-final after coming through a gruelling three-set encounter with two-time finalist Victoria Azarenka.

Second seed Halep was pushed all the way by the 20th seed and former world number one, whose aggressive approach made for an extremely entertaining affair.

But the 2014 French Open finalist came from a break down in the third set and brushed off the frustration of a lengthy rain delay to prevail 6-3 4-6 6-4.

The Romanian will now face Flavia Pennetta, who overcame Petra Kvitova in three sets, for a place in the final at Flushing Meadows.

Forehand and volley winners helped Azarenka break in the first game of the match but Halep - with heavy strapping on her right thigh - immediately responded and rattled off the next four games.

Azarenka recovered to help stem the tide but the Belarusian could not prevent Halep from taking a set lead, which was secured thanks two booming serves from the Romanian at 30-30 in the ninth game.

But Azarenka wasted little time in producing an emphatic response by breaking Halep's serve with a well-executed drive volley before consolidating to go 3-0 up.

Halep got things back on serve by taking the second of four break points at 3-1 down with a backhand winner, only to instantly surrender the initiative again with an off-target backhand.

The momentum soon shifted again, though, Azarenka failing to serve out the set at 5-3 as she dumped a forehand into the net.

Yet the match was sent to a third set in the next game courtesy of another wayward Halep backhand.

Azarenka looked to be on the brink of victory when she went 2-0 ahead as Halep sent a forehand long, yet the procession Azarenka will have hoped for did not arrive and Halep broke for a fifth time in the match before the rain halted her revival.

Halep quickly levelled at 2-2 upon the resumption, and the delay seemed to benefit both players as they each emerged with a renewed intensity.

However, Azarenka finally cracked and handed Halep the crucial break for a 4-3 lead with a backhand error.

And this time Halep would not be denied, with an overhit forehand from Azarenka finally settling a magnificent contest.