Felix, Farah head star-studded Prefontaine Classic athletics

British distance running king Mo Farah and US golden girl Allyson Felix headline a star-studded field as the Diamond Leagues Prefontaine Classic gets under way in Eugene on Friday with the World Championships looming on the horizon.

Farah, who completed an unprecedented 'double-double' of Olympic 5,000m and 10,000m gold at last year's Rio Games, will take to the track at the University of Oregon's Hayward Field with a fresh gust of doping intrigue swirling around coach Alberto Salazar.

Salazar, the mastermind of Nike's Oregon Project where Farah trains, has been implicated in a damning report by the United States Anti-Doping Agency (USADA) which has cast a critical eye over methods used by the coach.

The 269-page report accuses Salazar of dangerously using drugs to boost the performance of his athletes, concluding the coach had "almost certainly" broken anti-doping rules by experimenting with infusions of the amino acid L-carnitine.

Farah angrily hit out at the suggestion of involvement in doping when the revelations first emerged in February, insisting he had nothing to hide.

"I am a clean athlete who has never broken the rules in regards to substances, methods or dosages and it is upsetting that some parts of the media, despite the clear facts, continue to try to associate me with allegations of drug misuse," Farah said in February.

The full USADA report however was leaked to US outlets and published on the Internet this week, guaranteeing a fresh round of scrutiny as the third stop on the Diamond League season begins on Friday.

Farah faces a repeat of his Rio 5,000m final, with both silver medallist Paul Chelimo and bronze medallist Hagos Gebrhiwet, 23, in the field.

With August's World Championships in London coming into view, Eugene's powerful field will offer a preview of some of the rivalries that are likely to be on show in three months' time.

World record tilt?

Friday's night's opening events will see Ethiopia's Olympic silver medallist Genzebe Dibaba take another crack at the world record in the 5,000m, aiming to beat the existing mark of 14min 11.15sec held by her sister Tirunesh since 2008.

The highlight of Saturday's events sees what is being billed as the strongest women's 200m field ever assembled, with Olympic champion Elaine Thompson of Jamaica heading the line-up.

Thompson, who also won the 100m in Rio, is joined by her fellow Olympic 200m medallists, Dafne Schippers of the Netherlands and Tori Bowie of the United States.

The powerful lineup is given a sprinkling of stardust by the presence of US sprint queen Felix, the most decorated female track and field athlete in Olympic history.

The six-time Olympic gold medallist was unable to defend her 2012 200m crown in Rio last year after failing to qualify for the event at the US trials as she battled back from injury.

But the 31-year-old has opted to focus on the 200m this year and will get the chance to measure her progress against Thompson, Bowie and Schippers, who own three of the four fastest times over the distance this year.

Other highlights on Saturday include the men's 100m, where Olympic silver medallist Justin Gatlin and Canada's bronze medallist Andre DeGrasse resume their rivalry.

The women's 800m meanwhile sees Olympic champion Caster Semenya head a strong line-up which also includes Rio medallists Francine Niyonsaba of Burundi and MargaretWambui of Kenya.

The field events sees another Rio rematch in the men's pole vault, where Brazil's Olympic champion Thiago Braz faces France's Renaud Lavillenie and Sam Kendricks of the United States. Canada's 2015 world champion Shawn Barber, who flopped in Rio with a 10th place finish, is also in the field.