The American had been 0-10 in her career against top ten opponents before earning the come-from-behind win. Townsend came to net 106 times in the match, winning 83 of those points and will now face Sorana Cirstea in the third round.
Townsend serves and volleys her way to huge upset
Townsend came out as the aggressor and she earned a break point in the third game following a stunning backhand return. Halep forced the American to net her return and a second chance came and went, Halep holding for 1-1.
Following a nervy hold by the American, Halep kicked it into full gear, crushing a winner that Townsend was unable to return, breaking for a 3-2 lead. A love hold was followed by a second break, the Romanian benefitting from Townsend's error.
Serving for the set at 5-2, Halep races to a 40-0 lead to bring up three set points. She only needed one when Townsend meekly netted a backhand to give the reigning Wimbledon champion a one-set lead.
Townsend maintained her aggressive nature as she sought an immediate response and after another lovely volley, Halep's lob was over the baseline and the qualifier led 2-0. The Romanian broke back straightaway only to suffer another break.
More outstanding volleying by Townsend lifted her to a 4-1 lead and she would comfortably close out the set to square the match at one set all. In the third set, the Romanian nudged ahead 2-1, but still showed her frustration by thumping her racket against the court three times.
The American continued her all-out assault and it paid off for her as she broke Halep to take a 3-2 lead and then consolidated the break after digging out of 0-40 to hold for 4-2. She moved to the edge of victory with a 5-3 lead. It became 5-4 after a Halep hold.
Serving for the match, the American built a 40-15 lead, but a double fault and Halep winner brought the game to deuce. Four points later, the Romanian was level after firing off another winner. A subsequent hold now put Halep on the edge of victory.
Undeterred, Townsend staved off a match point to hold and force a tiebreaker. She built a quick 2-0 lead, only to see the fourth seed peg her back repeatedly. With honors even at 4-4, Halep duffed a forehand, missed a backhand and on match point, barely got her final backhand to the net to seal a victory Townsend would never forget.