Jenny Simpson becomes first American to medal in women's 1,500m

RIO DE JANEIRO, Aug 16 (Reuters) - Kenya's Faith Kipyegon won the women's Olympic 1,500 meters on Tuesday after unleashing a devastating second half of the race to leave Ethiopia's world record holder Genzebe Dibaba trailing in her wake.

Kipyegon, fastest in the world this year, sat in the pack as the runners virtually jogged the opening stages before she and Dibaba took off and pulled clear after a 56.8-second lap around the halfway mark scattered the field.

Dibaba, who has struggled with injury this year, led with 200 to go but the 22-year-old Kipyegon forced her way past and drove for the line to win in four minutes 8.92 seconds and reverse the order from last year's world championship final.

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"It was an amazing race," Kipyegon told reporters. "I needed to focus for the middle because I knew Genzebe is so fast and I really had to kick on the last lap."

Dibaba held on for silver, with American former world champion Jenny Simpson taking bronze.

Fellow American Shannon Rowbury finished fourth to suffer more frustration after being cheated out of a medal four years ago when finishing sixth.

The 2012 event in London has been dubbed the "Dirtiest Race in History" after six of the top nine, including the gold and silver medallists, committed doping offenses before or after the event.

Winner Asli Cakir Alptekin is serving an eight-year ban for her second offense while fellow Turk Gamze Bulut, who had improved her personal best by an eyebrow-raising 18 seconds, is also suspended.

There was also a cloud hovering over this year's race following the arrest in June of Jama Aden, Dibaba's coach, after an anti-doping raid, though the Ethiopian has never failed a test.

After her stellar 2015 Dibaba struggled with injuries this season but seemed to be running into form as she qualified fastest for a showdown that contained eight of the women who contested the world championship final in Beijing last year.

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It did not seem like that as they jogged through the first lap in 76 seconds and went through 800m in a pedestrian 2:27.21.

Dibaba then pressed the accelerator, however, and only Kipyegon and Briton Laura Muir could respond.

The Ethiopian led at the bell but her diminutive rival sat perfectly poised on her shoulder before driving clear in a 58.79-second last lap.

Muir faded, allowing the American duo to battle it out for bronze.

(Editing by Ed Osmond)

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