Three team mates of defending champion Jonas Vingegaard crashed when Sepp Kuss hit the spectator's arm and lost his balance.
Frenchman Alaphilippe retains lead.
'I just want to thank the whole team ... everybody it took to get to here.'
Britons David Millar and Bradley Wiggins will be the riders to watch when the Tour de France starts with a 7.9-km prologue in London.
All team members, riders and staff had until 1100 GMT on Monday, the Tour's first rest day, to take a test in the mobile laboratory provided by organisers.
The Italian outsprinted two fellow breakaways to claim the 197-km 18th stage of the Tour de France from Morzine to Macon.
German Andre Greipel was again far too strong for the opposition as he claimed his second win in this year's Tour de France.
Germany's Andre Greipel timed his final burst to perfection to win the sixth stage of the Tour de France on Thursday when South Africa's Daryl Impey became the first African to wear the yellow jersey.