Toronto: Swiss teen Belinda Bencic outlasted Simona Halep to win Sunday’s WTA Rogers Cup final when the Romanian second seed retired trailing 7-6 (7/5), 6-7 (4/7), 3-0.

Bencic, who upset world number one Serena Williams in the semi-finals, broke twice to open the third set before the effort of battling in extreme heat and humidity proved more than Halep could take.

The Swiss 18-year-old has won 21 of her last 25 matches and defeated four top-10 foes this week, improving to 6-1 this year against such high-ranked rivals.

It was the second career WTA crown for Bencic, whose first came in June at Eastbourne, and it capped an impressive week in which she defeated six Grand Slam finalists -- Eugenie Bouchard, Caroline Wozniacki, Sabine Lisicki, Ana Ivanovic, Halep and Williams, winner of the past four Grand Slam events in a row.

Bencic will jump to 12th in the world rankings after starting the week 20th, improving her position for the US Open, the year’s final Grand Slam event that starts August 31 in New York.

Halep and Bencic exchanged breaks over the first five games of the match before Bencic held for a 4-2 edge.

The 18-year-old double faulted to surrender an equalising break in the eighth game as the two battled into the tie-breaker.

Halep, who had her left leg treated in the final changeover before the tie-breaker, seized a 4-1 lead but Bencic fought back to win six of the last seven points to claim the first set, the last when Halep netted a forehand.

After an early exchange of breaks in the second set, Bencic broke for a 4-2 lead and Halep, taking treatment for the extreme heat at humidity, seemed near the end.

But she broke back to 4-3 and answered when Bencic broke for a 5-3 edge, breaking back again at love when the Swiss was serving for the match to pull within 5-4.

Halep held and broke again for a 6-5 lead and then it was her turn to serve for the set, but Bencic broke back to force the second tie-breaker.

Winning six points of seven, Halep seized a 6-2 edge and rallied from a weak stretch for the third match in a row to level matters.

But Halep, who beat Bencic in straight sets at Wimbledon a year ago in their only prior meeting, did not have a second wind and Bencic dominated her twice in service games before Halep called it quits, only her fourth loss in 32 hardcourt starts in 2015.