LAUSANNE - Justin Gatlin shot arch-rival Usain Bolt a warning with a consummate performance in his 26th successive sprint victory on Thursday, while Mo Farah returned to the track with a sublime win he said answered his critics. Gatlin, the 2004 Olympic 100m gold medallist and 2005 double world sprint champion who consequently served two doping bans before nailing the 2012 world 60m indoor title, Olympic bronze at the London Games and a world silver in Moscow a year later, is peaking perfectly for next month's world champs in Beijing.

At the age of 33, there is no doubt the American is currently the sprinter to beat, and at the Diamond League meet he saw off his two closest rivals this season in teammate Tyson Gay and Jamaican Asafa Powell. A smart start and impressive drive phase from 60 metres through to the line saw him clock 9.75 seconds, with Powell edging Gay for second, both timing 9.92sec.

"I used this as a semi-finals and Monaco (next week) will be a final, then I'll go home and get ready for the world championships," said Gatlin. "No disrespect, I went into the race not thinking about my opponents, I just wanted to execute my phases. I had a traditional fast start, tried to dominate through the middle and carried on through to the finish line and that's what I did. There's no message to Usain, I just go out there and try and dominate."

There was a dramatic season debut in the men's 5,000m for Olympic and double world champion Farah, his first outing since doping allegations against his coach Alberto Salazar. Farah held his nerve to kick back in a supreme show on the final lap from 80 metres out to beat Ethiopian Yomif Kejelcha. "This victory is also a way to answer some of the critics regarding my coach that came out lately," said an emotionally-charged Farah.

Claims made by BBC Panorama and US investigative website ProPublica alleged that Salazar broke doping rules by administering testosterone to American distance runner Galen Rupp in 2002 when Rupp -- a training partner of Farah -- was only 16, and encouraging misuse of prescription drugs. Salazar has refuted the claims, and Farah was not implicated for any wrongdoing, insists he is "100 percent clean" and has welcomed subsequent probes by both the British and US anti-doping agencies to help clear his name.

"The last couple of weeks have been hard for my family and everyone else. But what can you do? You just want to run and that's what I did and I enjoyed it," Farah said. One of the stand-out events at the August 22-30 Beijing worlds will surely be the men's triple jump, with world silver medallist Pedro Pablo Pichardo of Cuba and Olympic champion Christian Taylor pushing each other to their limits.

In another outstanding competition, American Taylor sailed out to 18.06 metres, the Cuban content with second (17.99m) as both consistently nail jumps around the 18m mark in search of Jonathan Edwards longstanding world record of 18.29m.

There was no joy for Kenya's David Rudisha in the 800m, the Olympic champion and world record holder edged into second by Botswana's Nijel Amos, who clocked a season's best of 1:43.27.

A strong US track presence was boosted by victory for Allyson Felix in her preferred 200m, having already garnered 2012 Olympic gold, two Olympic silver medals, and three world championship golds. "It's the 200m and I love this race, it's always my favourite," said the 29-year-old after her 22.09sec win, with Dutchwoman Dafne Schippers in second (22.29).

Dawn Harper-Nelson earlier led an American cleansweep of the women's 100m hurdles, her 12.55sec seeing off teammates Jasmin Stowers, Queen Harrison and Sharika Nelvis. But Shaunae Miller of the Bahamas, in 49.92sec, dominated the women's 400m, denying further American joy with Olympic champion Sanya Richards-Ross in second (51.12). Germany's reigning two-time world shot put champion David Storl fired out a warning ahead of Beijing with a personal best and meet record of 22.20m to beat American duo Joe Kovacs (21.71) and Reese Hoffa (21.30).