Peter Sagan won his third stage of this Tour de France, while Geraint Thomas kept the overall lead over teammate Chris Froome on Friday.

World champion Sagan won a sprint finish by a wheel length to claim Stage 13, a 169.5-kilometer (105-mile) leg from Bourg d'Oisans to Valence in less than four hours.

After overzealous fans marred Thomas' win on Thursday atop the Alpe d'Huez, the otherwise complete calm of Friday's leg was briefly disturbed by a man on the roadside who tossed a smoke bomb into the center of the peloton as it passed by with 16 kilometers left.

Besides spitting out yellow smoke, the bomb appeared to do no harm.

Thomas took charge of the race with impressive wins atop summit finishes on the previous two days.

The Welsh rider for Sky had no trouble maintaining his advantage of 1 minute, 39 second over defending champion Froome on the flat ride that came after three grueling days in the Alps.

Both Team Sky riders finished safely in the pack with their top rivals.

Tom Dumoulin stayed third overall at 1:50 behind. Primoz Roglic was fourth at 2:46, and Romain Bardet was fifth at 3:07 back.

Sagan timed his move perfectly, charging forward to overtake runner-up Alexander Kristoff and Arnaud Demare, who finished third, at the finish line.

The Slovakian's 12th career Tour victory came after he dominated sprints at the end of Stages 2 and 5.

This time, Sagan was racing against a field of top sprinters who had been greatly depleted by the mountains.

Fernando Gaviria and Dylan Groenewegen, who both won two stages on this Tour, along with Andre Greipel all abandoned the race on Thursday, while 30-stage winner Mark Cavendish and Marcel Kittel failed to make the time cut on Wednesday.

On Thursday's action-packed ascent up Alpe d'Huez, contender Vincenzo Nibali was forced to abandon the race after he broke a vertebra when knocked to the ground by a police motorbike tasked with keeping back the pressing fans.

Froome also was pushed hard in the back by a spectator, and Thomas was booed on the podium by fans who are skeptical of Froome's clearance from doping allegation just before the Tour's start.

Michael Schaer of BMC was the last rider of a four-man breakaway to be reeled in with 6K left.

Saturday's Stage 14 is a hilly 188-kilometer trek from Saint-Paul-Trois-Chateaux to Mende as the race makes its way to the Pyrenees Mountains.