Colombian Santiago Buitrago took the first mountain stage of Paris-Nice on Wednesday after an exhilarating finish in the Beaujolais wine-growing region that went down to the last kilometre.

The 183km fourth stage from Chalon-sur-Saone to Mont Brouilly featured six category two climbs and a category one in the shape of the 7.3 percent Col du Fut d'Avenas, 20km before the finishing line.

"I really did not expect this... To win a World Tour race here in France is exceptional for me," said Buitrago.

"I had good legs and a good breakaway companion with (Luke) Plapp who helped me into the finale. I'm also well placed in the GC (general ranking) so it's great."

Going pedal to pedal with Luke Plapp of Jayco AlUla, Team Bahrain's Buitrago claimed the imposing 3km final ascent of Mont Brouilly to take his first ever Paris-Nice stage victory.

Mathieu Burgaudeau and Christian Scaroni broke away from the leading pack on the ascent of Col de Durbize, with just over 50km left to race, before the Italian showed the Frenchman a clean set of wheels to streak out on his own as the summit approached.

Scaroni sat out just in front until the stage's daunting Col du Fut d'Avenas climb on the 161km mark, where Buitrago and Plapp attacked to take the lead.

The pair battled it out neck-and-neck over the stage's last 20 kilometres until the Colombian found a final burst on the last ascent to leave his Australian competitor behind and claim the win.

Despite coming second, Plapp claims the overall leader's jersey from Brandon McNulty, who drops into third just behind stage-winner Buitrago.

Frenchman Burgaudeau of TotalEnergies held on to the polka dot jersey as the race's best climber and increased his tally to 28 points, seven ahead of Scaroni in second place.

Remco Evenepoel of Quick-Step, one of the favourites to win the race, attacked twice in the last kilometre to finish fourth in the stage and move up to fifth in the general ranking.

Evenepoel went head-to-head with rival Primoz Roglic in the stage's intermediate sprint and the Belgian emerged victorious, picking up six seconds to the Slovenian's four.

Egan Bernal of Ineos and Bora's Roglic finished fifth and seventh respectively on the day. Former Tour de France and Giro winner Bernal is sixth overall, 40 seconds behind Plapp, with Roglic another 30 seconds back in 15th.

Inclement weather is forecast to set in over the weekend and the penultimate stage of the race on Saturday could be modified with snowfall expected at the finish line in Auron.

"It could be complicated, but we have to wait for more precise forecasts to know exactly what we have to do," Thierry Gouvenou, event director for Amaury Sport Organisation (ASO), said to AFP.

"We have the advantage of leaving early and the weather is only forecast to be difficult at the end of the day."