Fourth seed Simona Halep suffered a shock second-round loss to world number 116 Taylor Townsend at the US Open.

American Townsend, 23, won 2-6 6-3 7-6 (7-4) to reach the third round at Flushing Meadows for the first time.

Wimbledon champion Halep, 27, cruised through the opening set but showed her frustration in the third by hitting her racquet on the ground after a miss.

In a thrilling final set, Halep had a match point before qualifier Townsend won in a dramatic tie-break.

An emotional Townsend said: "This means a lot. It's been a long journey. I had a match point against Kiki Bertens at Wimbledon and close matches this year and not managed to get over the hump.

"This match gives me so much confidence that I can do it. When I've played Halep before I tried to make balls and played not to lose. Today I played to win.

"I said to myself this was an opportunity to go for it. There was nothing to lose."

In front of a large crowd at Arthur Ashe Stadium, it looked like being a routine win for former world number one Halep.

But Townsend fought back with an attacking serve-volley game that saw her move into the net more than 100 times.

She had missed two match points at 5-4 in the final set, double-faulting on the first opportunity before Halep produced a fine down-the-line forehand winner on the second.

The Romanian also had her own chance to win it, but wasted it when she went long with a forehand as Townsend again ran into the net.

In the tie-break, Townsend was never behind and from 4-4 then won the final three points to book her place in the next round.

She will play another Romanian, Sorana Cirstea, who also came from a set down as she beat Spain's Aliona Bolsova 3-6 6-4 6-2.