Britain's Mo Farah won the 5,000m at the Diamond League in Lausanne, his first race since doping claims against his coach Alberto Salazar.
The 32-year-old double Olympic champion won in 13 minutes 11.77 seconds.
Last month BBC Panorama and US investigative website ProPublica made claims that Salazar violated several anti-doping rules.
"This is a way to answer some of the critics regarding my coach," said Farah, who says he is "100% clean".
|Selected winners in Lausanne|
|Men's 100m: Justin Gatlin (US) 9.75 seconds||Women's 100m hurdles: Dawn Harper-Nelson (US) 12.55 seconds|
|Men's 200m: Zharnel Hughes (GB) 20.13||Women's 200m: Allyson Felix (US) 22.09|
|Men's triple jump: Christian Taylor (US) 18.06m||Women's high jump: Anna Chicherova (Rus) 2.03m|
The race was Farah's first for six weeks and his first at 5,000m this season.
He faced a strong field including 17-year-old Ethiopian Yomif Kejelcha, who has run the fastest time this year - 12:58.39.
Farah sprinted past the teenager with 300m to go and began wildly celebrating down the home straight before crossing the line.
He told BBC Sport: "Training's been going well, the race was loaded, you had everybody in it.
"I've answered all the questions as an athlete and all I want to do now is do what I do best and run and enjoy it."
British rival Andy Vernon later claimed that Farah swore at him after snubbing a handshake.
Farah had pulled out of a Diamond League meeting in Birmingham last month following the claims against Salazar.
The athlete has not been accused of any wrongdoing and has welcomed subsequent investigations by UK Anti-Doping and the US Anti-Doping Agency.
Salazar has denied the allegations and issued a 12,000-word document refuting claims made in the investigation.
Farah is due to race over 1500m in Monaco on 17 July before returning to the Olympic Stadium in London to compete in the 3,000m at the Anniversary Games the following week.
He will then defend his 5,000m and 10,000m titles at the World Championships in Beijing in August.
|Analysis - ex-GB sprinter Darren Campbell|
|"Times don't matter when the field is full of rivals you will potentially meet at the World Championships. The most important thing to do on an evening like this is to win. For a lot of these athletes competing against Mo Farah they would have felt if there was a chink in his armour it would have been exposed, so he has got rid of that one and now they will have to deal with that at the World Championships."|
Farah's victory in Lausanne was followed by American Justin Gatlin running 9.75 seconds - the joint second-fastest time of 2015 - to beat Asafa Powell and Tyson Gay in the 100m.
Anguilla-born Zharnel Hughes ran a personal best 20.13 to win the 200m, just over two weeks after becoming eligible to race for Britain.
The 19-year-old qualified for the World Championships with victory at the British Championships last month.
Olympic champion Christian Taylor beat the meet's triple jump record with a leap of 18.06m, the fourth longest of all-time.
The American became only the second athlete - after Britain's Jonathan Edwards - to go beyond 18m twice in the same meeting.
Edwards jumped 18.16 before breaking the world record with a leap of 18.29 at the 1995 World Championships in Gothenburg.
Commonwealth 800m champion Nijel Amos strode past Olympic champion and world record holder David Rudisha in the closing stages of a race in which the pair - gold and silver medallists at London 2012 - were well clear of the opposition. The Botswana athlete clocked 1:43.27 and has now beaten Rudisha on each of their five meetings since London.
Olympic champion Allyson Felix won the women's 200m in 22.09 seconds while Russian Anna Chicherova won the women's high jump with the best jump of the year - 2.03m.
Britain's Anyika Onuora (51.26 seconds) was fourth behind Shaunae Miller (49.92) in the 400m - both times were personal bests.
British and European champion Tiffany Porter (12.66) was fifth in the women's 100m hurdles behind former Olympic champion Dawn Harper-Nelson (12.55).