BRUSSELS — Apart from the celebrations of Eddy Merckx's first victory at the Tour de France half a century ago, nothing went according to plans on the race opening day.

In cycling-mad Belgium, defending champion Geraint Thomas was caught in a crash Saturday and toppled over his handlebars in the finale of the first stage. The race leader's yellow jersey ended on the shoulders of a relatively unknown rider who switched from zealous teammate to ace sprinter.

After the pile-up tore the peloton apart and played havoc with sprinters' teams, Mike Teunissen posted the biggest win of his career with an unexpected yet remarkable stage win at the expense of former world champion Peter Sagan, the king of sprints in recent years at the Tour.

Caleb Ewan, an up-and-coming sprinter, took third place on the finish line in Brussels.

The first days of the Tour are always tense and marred by race incidents, and this year's race is not going to be any different.

"The finale was not dangerous," Teunissen said after an impressive burst of power in the final meters that allowed him to pip Sagan. "It's only because the riders were nervous that it was dangerous."

The opening day stage could have turned into another nightmare for Thomas' Ineos team, which is already without four-time champion Chris Froome. The British rider was ruled out of the Tour last month after suffering multiple career-threatening injuries at a warmup race.

But Thomas escaped unscathed. The former track specialist was riding at the front of the race when the spill occurred and he bumped into barriers.

"I'm fine. It was pretty slow by the time I hit them," he said. "I gave myself enough space and avoided the actual crash but with the barriers there was nowhere to go. The main thing is that it didn't do any damage. This first week is all about just getting through."

Thomas's teammate Egan Bernal, another top contender, did not fall but was also held up by the crash. The pair did not lose time as per race regulations because the accident occurred within the final three kilometres.

Jakob Fuglsang, another favourite, also hit the tarmac about 20 kilometres (12 miles) from the finish in a separate crash. The Astana team leader remounted his bike with blood on his face and right knee, and tears on his jersey. He needed stitches for a cut above his right eye.

"I think he'll be ok," said Astana team director Alexandre Vinokourov. "First week in the Tour de France is always the most dangerous for the guys."

Teunissen, the first Dutch rider to wear the yellow jersey since Erik Breukink 30 years ago, showed solid nerves after the second spill took out of contention his Jumbo-Visma teammate Dylan Groenewegen, the team's best sprinter.

Teunissen was initially set to be part of Groenewegen's leadout train but quickly turned his focus to personal goals once his leader went down. In the slightly uphill section leading to the finish line on the leafy Avenue du Parc Royal, Teunissen perfectly timed his effort to deny Sagan a 12th stage win at the Tour.

"I thought all the work we had done for quite a long time was suddenly gone," he said. "But I felt good and thought I could maybe achieve a Top 5. I was relaxed, with nothing to lose. I opened up and I had a lot of power. It got me to second position and I saw Sagan was going slower than me. I threw myself at the line. Mission accomplished."

Teunissen did not get carried away with his win, though, and promised to keep working for Groenewegen if he recovers well.

"It's only unfortunate for Dylan, hopefully he is okay and can sprint again in a few days," he said. "Still, we have the yellow jersey in our room, it's really strange but also very nice."

Michael Woods of Ottawa was 87th while Hugo Houle of Sainte-Perpetue, Que., was 91st.

The 194.5-kilometre (120.8-mile) stage had started in a joyful mood in the heart of Brussels, with Merckx greeted by Belgian fans filling the streets as he stood alongside race director Christian Prudhomme in a red open-top car riding in front of the peloton. Leaving Brussels, the 176 Tour competitors started their loop south of the city at a fast tempo as a group of four riders led by Greg Van Avermaet, a one-day classics specialist from Belgium, immediately formed at the front.

The quartet reached the first difficulty of the day — the Muur van Geraardsbergen, a 1.2-kilometre cobbled climb — with a 3-minute lead. Van Avermaet made a point of honour to be first at the top to the delight of home fans cheering him along on the side of the road. Belgian rider Xandro Meurisse, a member of the initial breakaway, was first at the Bosberg, another climb featuring at the Ronde van Vlaanderen classic race.

Guaranteed the first best climber's polka dot jersey, Van Avermaet stopped his effort soon after and was reined in by the peloton as the lead group was reduced to three men: Meurisse, Natnael Berhane and Mads Wurtz, who were caught with 70 kilometres left

Tour debutant Stephane Rossetto of France then tried a solo escape and was first at the Lion's Mound monument that overlooks the battlefield where Napoleon's troops were defeated at the Battle of Waterloo. But the Frenchman's efforts on open stretches of road exposed to wind were left unrewarded and he was ultimately swallowed up as the final sprint took shape.

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