LANDERNEAU, France, June 26 (Reuters) - A roadside spectator holding a cardboard sign caused a massive pile-up during the first stage of the Tour de France, which left several top riders being held up on Saturday, while another huge pileup with 7.5 km left brought down Chris Froome and others. In the first crash, German Tony Martin was sent tumbling when he rode straight into the sign, which said "Allez Opi-Omi" (Come on granddad-granny, in a mix of French and German) amid scenes of chaos with 47 km left. Overall contenders Tao Geoghegan Hart of Britain, as well as Colombian Miguel Angel Lopez, were among the riders being held up and lost considerable time on the opening day of the three-week race. Belgian Wout van Aert, one of the favourites for the stage win, was also slowed down but made it back to the main bunch after a long effort, just like eventual stage winner Julian Alaphilippe, who had blood dripping from his knee when he crossed the line. "I hope everyone is OK. I"m calling on the fans to be careful. It"s nice to see the fans back on the side of the road, but please be careful," said Alaphilippe. Cycling - Tour de France - Stage 1 - Brest to Landerneau - France - June 26, 2021 The peloton in action REUTERS/Stephane Mahe Cycling - Tour de France - Stage 1 - Brest to Landerneau - France - June 26, 2021 Deceuninck–Quick-Step rider Julian Alaphilippe of France in action before winning the first stage REUTERS/Stephane Mahe Cycling - Tour de France - Stage 1 - Brest to Landerneau - France - June 26, 2021 B&B Hotels p/b KTM rider Cyril Lemoine of France receives medical attention Pool via REUTERS/Anne-Christine Poujoulat 1/5 Cycling - Tour de France - Stage 1 - Brest to Landerneau - France - June 26, 2021 Deceuninck–Quick-Step rider Julian Alaphilippe of France in action before winning the first stage REUTERS/Stephane Mahe German Jasha Suetterlin of Team DSM was consequently the first rider to abandon the race after being sent to the ground by the crash. The second crash brought down Froome and many others including Marc Haller, Andre Greipel and Ion Izagirre as bikes were sent flying to the side of the road. Froome climbed back on his bike after being attended to by a race doctor but looked in considerable pain when he crossed the line 14:37 behind Alaphilippe. The Briton, a four-time Tour champion, was back on the race after missing the last two editions following a horrific crash in June 2019. Even before the crash he had little hope of winning the race, having failed to recover his best form.