An exceptional line-up of track and field stars offered up an evening of high-class competition at the packed Stade de la Pontaise in balmy, windless conditions.
Olympic champion Kirani James set the tone by scorching to the fifth fastest time ever run in the men's 400m, the Grenadian back to the form that saw him top the podium in London two years ago.
And then Gatlin trumped Gay in a scintillating 100m, the former clocking 9.80 seconds for victory. Only six men have run faster.
"There were definitely nerves there, first race back!" said the 31-year-old Gay, cleared to run after world athletics' governing body, the IAAF, announced last week that it would not appeal the reduced one-year sanction he served for testing positive for a banned anabolic steroid in two out-of-competition tests.
"I was a little bit nervous but got over that pretty quickly. Knowing what I've been through, I've been doing it for nine years professionally, I had to go back to old habits and focused on myself."
In the absence of Usain Bolt, still rehabilitating a leg injury, Yohan Blake was bearing Jamaican hopes of a sprint victory in the 200m.
But those were also dashed as he could only finish sixth in a relatively pedestrian 20.48 seconds behind winner Alonso Edward of Panama, the 2009 world silver medallist streaking home in a very creditable 19.84 seconds.
In the 400m, 21-year-old Grenadian James led from gun to tape to win in 43.74 seconds, the season's fastest time around one lap and the fifth fastest time ever run. Only four Americans, headed by Michael Johnson, have gone quicker.
"I wanted to come out and give my best," said James. "The conditions were perfect, I'm very happy with my run.
"I feel in top shape and I would like to carry this form to the Commonwealth Games."
One athlete who should not have any problem sealing Commonwealth gold later this month is New Zealand's Valerie Adams.
Adams' imperious form continued as she notched up her 51st straight victory in the shot put, managing a best of 20.42m to once again easily beat her hapless rivals.
Kenya's Mercy Cherono also looked sharp, an impressive home-stretch sprint trumping fancied Ethiopian Genzebe Dibaba in the 3,000m in a conservative 8:50.24.
The high jump once again showed its star qualities, Ukraine's Bogdan Bondarenko winning with a best of 2.40m, but going close with three attempts at 2.46m, 1cm higher than Cuban Javier Sotomayor's 1993 world record.
French pole vault king Renaud Lavillenie, crowned world record holder earlier this season with a best of 6.16m, won the competition in Lausanne with 5.87m from Brazilian Thiago Braz (5.72).
It was also a good night for Lavillenie's team-mate Pascal Martinot-Lagarde, who won the 110m hurdles ahead of Russia's European champion Sergey Shubenkov, with Americans David Oliver and Jason Richardson, the two previous world champions, finishing fourth and seventh respectively.
The Swiss 4 x 100m women's relay team were also celebrating after setting a new national record of 42.94 seconds.