Italian rider Elia Viviani finished second ahead of Lotto - Soudal's Ewan and Team Sunweb's Matthews in Monday's Saint-Flour to Albi stage.

Julian Alaphilippe of France kept the yellow jersey after contenders including Australian Richie Porte became trapped in an echelon in the final kilometres.

A day before the first rest day, crosswinds caused the peloton to stretch and break up during the last 35km of the 217.5km trek in southwestern France.

Defending champion Geraint Thomas reached the finish line in the main pack but Porte and other favourites were caught off guard and lost time.

Porte was in a group including Frenchman Thibaut Pinot, Rigoberto Uran and Jakob Fuglsang that lost 1 minute and 40 seconds.

The peloton split into three groups on a long but narrow section of road open to the wind when Alaphilippe's Deceuninck Quick Step teammates sped up the pace at the front to close the gap to six breakaway riders.

The fugitives were brought in with 25km left before Thomas's Ineos teammates, working well with Alaphilippe's team, pushed harder in an impressive display of collective strength.

"I couldn't think of anything better," Thomas said.

"It's especially good on a day like today when you never expect it. It was just a positioning error from them and they lose a minute and a half. That's how it goes."

Pinot used an expletive to describe his day.

"What do you want me to say? There's nothing to say," he said.

Thomas moved to second place overall, 1:12 behind Alaphilippe, with teammate Egan Bernal in third place, four seconds further back.

Britain's Adam Yates, riding for Australian team Mitchelton-Scott, goes into the rest day in seventh place overall.

Van Aert, a three-time cyclo-cross world champion, is riding his first Tour de France after claiming two stage wins - a sprint and a time trial - at the prestigious Criterium du Dauphine in June.

"The last 70km were very nervous," Van Aert said after edging Viviani by just a few inches.