The Slovakian, a triple road race world champion, triumphed after a sprint to win stage 13, a flat 169.5 kilometre route from Le Bourg-d'Oisans to Valence.

He had previously won stages two and five and has increased his grip on the green points jersey which he has won five times.

Sagan left it late to strike but the Bora-Hansgrohe rider defeated Alexander Kristoff, of Norway and UAE Team Emirates, and Arnaud Demare of France and Groupama-FDJ in a bunch finish.

Team Sky's Thomas was able to finish in the pack to maintain his lead of 1min 39sec over Team Sky team-mate and fellow Briton Chris Froome.

Sagan timed in at 3 hours 45min 55sec.

Froome, the defending champion and Thomas' colleague at Team Sky, is hoping to win the race for the fourth time in a row and also holds the two other Grand Tours, the Vuelta a España and the Giro D'Italia.

However, it is now up for debate who Team Sky will ride for after the form of Thomas, who won two consecutive stages before today.

Meanwhile, race director Christian Prudhomme has "called for calm" after incidents involving fans during this year's race.

Froome, who was cleared of an anti-doping violation on the eve of the race, appeared to be shoved and spat at during yesterday's stage to Alpe d'Huez which also saw former champion Vincenzo Nibali of Italy withdraw injured after he was knocked from his bike.

The Bahrain-Merida man has reportedly fractured a vertabrae. 

"We need to restore calm and respect all the riders," Prudhomme said. 

"It was a very annoying climb of Alpe d'Huez. 

"The riders on the Tour, and champions of the Tour, must be respected, as they are by the large majority of the public."

Tomorrow's stage is a 188km route from Saint-Paul-Trois-Châteaux to Mende.