TORONTO, Canada (AFP) - Thailand's Ariya Jutanugarn drained a 25-foot birdie putt to win the Manulife LPGA Classic in a three-way playoff Sunday, guaranteeing her ascent to the world number one ranking.

Her dramatic win at Whistle Bear Golf Club in Cambridge, Ontario came after rival Lexi Thompson stumbled with four bogeys on the back nine which saw a four-shot lead evaporate.

On the first playoff hole, Thompson looked to have recovered her composure when she crushed a long tee shot 50 yards further than Ariya and South Korea's Chun In-Gee.

Ariya, who had underhit her tee shot into the fairway rough, hit her second onto the green.

Both Chun and Thompson then missed long birdie putts leaving Ariya with her shot at glory which she duly converted.

The result capped a rollercoaster week for the 21-year-old from Bangkok, who had wrongly been informed by the LPGA last week that she had taken the world number one ranking.

The LPGA later revealed she had not in fact taken the top spot from New Zealand's Lydia Ko because of a rankings miscalculation.

Thompson meanwhile was left reflecting on her third defeat in a playoff this season after she looked to be cruising to her second title of the year.

Thompson, 22, had opened up a four-shot lead by the 11th hole.

But back-to-back bogeys on the 12th and 13th holes gave her rivals hope before Thompson recovered with a birdie on the par-four 15th.

However a three-putt on the par-three 17th set up a tense finale with Thompson one shot clear.

After making the green in regulation, the American was left with two putts to win.

But her birdie putt rolled up short, leaving her with a four-footer for victory which she then missed, setting up the playoff drama.

Ariya had entered the playoff after a three-under-par final round 69 while Chun forced her way into contention with a two-under-par 70.