"In cycling, you can support a rider without booing the others".
There had been fears about security on Alpe d'Huez with Froome still facing lingering ill-feeling among some cycling fans following the salbutamol case in which he was cleared of wrong-doing just days before the Tour began, while Sky have often faced a mixed reception in France due to their dominance of the Tour in recent years.
"We've got two cards to play and it's good for our strategy, " Sky sports director Nicolas Portal said before Friday's stage.
Fans camping out on Huez for weeks before the race create a raucous atmosphere. I want the fans to respect the riders.More news: Trump to formally invite Putin to U.S. , startling national security director
"It's great for us that all of these fans are there, it really motivates you. They make the riders breathe in noxious air, and they blind them", he added.
Cycling's world champion did not disappoint, timing his move to reach maximum speed as he swung past two challengers to claim Stage 13 by a wheel length and take his third win of this race.
Geraint Thomas, the stage victor, overall leader and Froome's Team Sky teammate, was booed both as he crossed the finish line and stood on the winner's podium, and now Tour director Christian Prudhomme has had just about enough.
Defending champion Chris Froome, who has often been subjected to negative treatment from Tour de France fans, was booed all the way up to the summit and one spectator ran alongside the Briton before slapping him on the shoulder.
Both Team Sky riders finished safely in the pack with their top rivals.More news: Olivia Munn is not a fan of Samantha Markle
Sagan, meanwhile, took his third victory of the race as he outsprinted Alexander Kristoff (UAE Team Emirates) and Arnaud Demare (Groupama-FDJ) in Valence.
On stage 12, Geraint Thomas got a gap on his rivals with a sprint to the line.
This time, Sagan was racing against a field of sprinters greatly depleted by three gruelling days in the mountains.
Twenty-four hours after four-time victor Chris Froome was slapped and apparently spat at by elements within the massed crowds on Alpe d'Huez, there was fresh trouble when a spectator threw the flare around 16 and a half kilometres before the finish of the 169.5km stage from Bourg d'Oisans.More news: Alisson's transfer to Liverpool 'at a very advanced stage,' says Roma