Mo Farah has triumphed in the 5,000 metres at the Prefontaine Classic after running the fastest time in the world this year.

The 29-year-old ran 12 minutes 56.98 seconds in the Diamond League event in Oregon to deliver a timely boost to his hopes of landing Olympic gold in London.

Farah shaved less than four seconds off his British record to beat Ethiopia's Isaiah Koech into second place, while his American training partner Galen Rupp came in third.

"The crowd got behind me. I was really pleased. It was awesome," said the 5,000m world champion. "It was kind of an up and down pace. I started reasonably good then slowed down in the middle and then towards the end I picked it up again.

"The conditions were a little windy today so I wasn't as perfect as what I wanted. But at the end of the day, I think the most important thing was to get a win under my belt."

Despite recent success over the distance, Farah has not yet committed himself to the event at the London Games, and has instead set his sights on the 10,000m race.

"I am going to run the 10,000 for sure because it is the first race," Farah added. "I will see how I feel after that. It depends how I come off in the 10,000. I would like to be fresh and not have any niggles."

Farah has now won his first four outdoor races of the season.