Farah kicked away from Ethiopia’s Yomif Kejelcha in the final 100 metres of the 5,000m race and punched the air as he crossed the line in 13 minutes 11.77 seconds.
It was a hugely impressive run against a stacked Diamond League field from an athlete who has seen his world turned upside down in the past five weeks by the doping storm surrounding his coach Alberto Salazar.
Farah, whose last race was 41 days ago, led with two laps to go, controlling the pace from the front, and was still in front at the bell.
Seventeen-year-old world leader Kejelcha moved past him with 300m to go, but the Briton’s most potent weapon is his finishing speed and when he moved up a gear down the home straight his Ethiopian rival had no answer, coming home in 13mins 12.59secs.
The pair finished well clear of the rest of a loaded field.
This was no easy return for Farah in his first 5,000m outing of the year, two of five fastest men in world this year, Ethiopia’s Hagos Gebrhiwet and Kenya’s Thomas Longosiwa, did not start.
He was back in at the deep end and, running in the distinctive black kit of the Nike Oregon Project, his elation at the line was plain to see.
Farah has been caught up in the doping allegations surrounding Salazar, who has denied claims made by BBC Panorama and US investigative website ProPublica that he violated several anti-doping rules.
The Briton, who has not been accused of any wrongdoing, has vehemently insisted he is ”100 per cent clean”, saying the allegations were ”killing” him and his family, but is sticking by his under-fire coach.
He said after Thursday’s win, in quotes posted on the Athletissima website: “I wanted to race everybody and today offered this opportunity. I had a great finish, overall I am happy with the way the race went.
“This victory is also a way to answer some of the critics regarding my coach that came out recently.”
A turbulent period for Farah, who has been training at Font Romeu in the Pyrenees, has clearly not affected his focus, though.
His form and fitness look spot on with six weeks to go before the World Championships in Beijing, where he will look to defend his 5,000m and 10,000m titles.
He will face another test when he races over 1,500m in Monaco in eight days’ time before returning to the Olympic Stadium in London to compete over 3,000m at the Sainsbury’s Anniversary Games the following week.
Earlier in the evening there was a landmark win for 19-year-old Zharnel Hughes in the 200m.
The 19-year-old Anguilla-born sprinter, who was cleared to compete for Great Britain last month, ran a superb bend from lane two and held his form down the home straight to win in a new personal best 20.13.
It made him the first British athlete to win a 100m or 200m race at a Diamond League event.
Hughes, who trains alongside Usain Bolt in Jamaica and won the British title last weekend, said: “I am very happy today with my new personal best, but even more excited to see what times I will run in the remaining weeks.”
Justin Gatlin underlined his status as the world’s dominant sprinting force, though, as the two-time drug cheat crushed Asafa Powell and Tyson Gay to win the 100m in 9.75.
American Christian Taylor equalled the Diamond League record as he leapt 18.06m to win the triple jump.
Elsewhere, there was a new personal best for Anyika Onuora, who clocked 51.26 to finish fourth in the 400m, Shara Proctor was second in the long jump and Tiffany Porter fifth in the 100m hurdles.