LONDON (REUTERS) - Kenyan Hellen Obiri produced an astonishing last lap to leave defending champion Almaz Ayana in her wake as she won the women's 5,000 metres at the World Athletics Championships and claimed her first major title on Sunday.

Ethiopia's Ayana, who led Obiri for more than half the race, was denied a double after winning the 10,000 metres with a devastating run earlier at the championships.

The pair broke clear of the pack after one third of the race and opened up a huge gap as they set a blistering pace.

Ayana led with Obiri on her shoulder into the final lap until the Kenyan, silver medallist in Rio de Janeiro last year, burst past with 300 metres left and stormed home to win in 14:34.86, more than five seconds clear of her rival.

Sifan Hassan of the Netherlands prevented an East African clean sweep by taking the bronze. "I was telling myself to go. I could see Ayana was not going so I thought, why not?" said Obiri. "I am mentally strong so I knew I was capable."

It was always going to be an enthralling contest.

Obiri, 27, has steadily moved closer to a major title over the course of he career and had won all of her races this summer over 5,000 metres, clocking the fastest time of the year when she ran 14:18.37 in Rome.

Ayana was bronze medallist over the distance in Rio where she also won the 10,000 metres and set a world record. She has been plagued by injury this season and the 10,000 race on Aug.5 was her first of the season.

Obiri did not run the 10,000 metres last week and her decision to concentrate on the shorter distance paid off.

There was a cagey start with the first 400 metres taking a painfully slow 81 seconds before Ayana and Obiri took control.

Ayana seized the initiative with nine laps left, Obiri followed and after steadily increasing the gap, they were more than 50 metres clear with four to go.

The Ethiopian tried several times to pull away but Obiri responded each time before producing her deadly final push.

"It was a difficult race. I am better at leading it to get the win rather than challenging in a final sprint. It was difficult to push Hellen through to the finish line," said Ayana. "Compared to Rio this is a bigger achievement. I've had many injuries this year so I am very happy with two medals."