Belgian Merlier wins crash-marred Tour de France dash to Dunkirk
The stage was marred by a series of falls, but the two favourites for the title Tadej Pogacar and Jonas Vingegaard finished safely in the main pack and remain in second and third place overall behind Van der Poel.
The flat 179km run from Valenciennes along the Belgian border was marked above all by a nasty fall that caused Jasper Philipsen to quit with severe grazing and a suspected fracture.
The fall happened during an intermediate sprint 60km away from Dunkirk and ripped the green best sprinter's jersey from Philipsen's back as he slid along the road in the 70kph crash.
Much of what Philipsen's team Alpecin had planned for the Tour revolved around the sprinter, team-mate Van der Poel revealed.
"It's always one of our goals to win stages so this is a bad day," the 30-year-old said.
Van der Poel suggested the wind had emboldened the sprinters.
"In a head wind it's easier to come from behind in the sprints, it made things more chaotic," he said.
There were three more falls, including two nasty looking ones in the finale with Olympic champion Remco Evenepoel, Merlier's teammate, involved.
'A mess'
Merlier, 32, grew up just over the border from Dunkirk and had been hoping to win the opening stage on Sunday.
"That was a mess," Merlier said of the falls. "I lost a great deal of energy getting in position but it was a good bike throw. I knew I'd beat Milan."
Lidl-Trek's Milan led over most of the final 150m, but even without sealing the stage win his efforts were still rewarded as he inherited the green sprint points jersey from the stricken Philipsen.
Van der Poel in the leader's yellow jersey is the grandson of French cycling legend Raymond Poulidor, who came second in the Tour de France seven times, but never won and never got to don the yellow tunic.
Another Belgian, the national champion Tim Wellens, gave cross-border fans even more to celebrate as he won the day's only climb, the 2.3km ascent of Mont Cassel at 31km from the finish line.
The 34-year-old will now hold the king of the mountains polka dot jersey overnight.
Frenchman Kevin Vauquelin is in the best under-25's rider's white jersey afer staying in the finishing mix in all three stages.
Regional police said one million spectators had lined the roadsides on the opening day, and while rain dissuaded that kind of turnout for stage two, huge crowds turned out again for the run to Dunkirk.
The eleven bikes stolen from outside the Cofidis team hotel early Sunday were all found before the stage's end -- five of them were recovered abandoned in a forest early Monday with the others being tracked down by the police later in the day.
Tuesday's fourth stage is a 174km run from Amiens, as the Tour leaves the North region, to Rouen in Normandy, with five hills in the final 25km designed to spark a series of race-splitting attacks.
The first section of the Tour is raced through the north and west of France.
The volcanic landscape of the Puy de Dome presents the first mountains as late as stage 10, with two more colossal climb days in the Pyrenees before the blockbuster final week in the Alps.