The Cofidis rider won in Willunga at the end of the penultimate stage, contested over 133.2 kilometers, ahead of the Italian Alberto Bettiol (EF Education EasyPost) and the Frenchman Hugo Page (Intermarche Circus Wanty).
Australian Jay Vine (UAE Team Emirates) maintained his lead of 15 seconds in the general classification over Briton Simon Yates (Team Jayco-AlUla) before the fifth and final stage, Sunday between Unley and Mount Lofty, over 112.5 km .
Coquard, who had 48 successes before Saturday, enthusiastically welcomed his advent into the World Tour.
"I've been waiting ten years for this victory, my first on the World Tour," said the 2012 Olympics omnium silver medalist.
"I'm very proud and very happy. I've won a lot of races, but never on the World Tour," said the 30-year-old native of Saint-Nazaire.
"That was the goal for 2023, so getting there in January is good news," said Coquard.
Well protected from gusts of crosswind by four of his teammates, Vine for his part preserved his ocher leader's jersey, even if he explained that he had lived "a very stressful day" with many attacks to watch.
"I don't sell the skin of the bear until I have killed it (...) but we can say that tomorrow is the day when we will have the strongest team for the arrival at Mount Lofty", said claimed the winner of two stages in the Vuelta last year.
On Sunday, the peloton will climb the short but steep summit of Mount Lofty five times on a circuit course above the city of Adelaide.
© 2023 AFP