Cavendish (Deceuninck - Quick-Step) came into the race as the big favourite for the sprint stages thanks to his amazing form in the French Grand Tour where he equalled Eddy Merckx's record of 34 stage wins and won his second green jersey.
However, the Manxman lost his main lead-out man and Olympic gold medallist Michael Mørkøv in the final 18km thanks to a mechanical, leaving his team-mates to try and place him in the best position.
This meant he had to surf the wheels in the closing stages, picking the wheel of Groenewegen (Jumbo-Visma) who was being led out perfectly by Mike Teunissen. But the finale around Esbjerg was very technical on tight roads with a mix of sharp and sweeping bends as well as patches of town cobbles and speed bumps.
Even the finish straight was tough with it being slightly uphill, also on town cobbles. Despite seeing the finish twice before the final sprint, Cavendish seemed over-geared going into the dash for the line with Groenewegen opening up a gap very quickly.
Cavendish was not able to catch the flying Dutchman but he did manage to hold off the advances of the European champion, Giacomo Nizzolo (Qhubeka-NextHash) to take second.
The front three gapped the rest of the peloton that was led in by Rally Cycling's Arvid de Kleijn.
The field is filled with some top names including two of Cavendish's team-mates Remco Evenepoel and Yves Lampaert, who are potential race favourites due to a hilly stage and a time trial.
Others such as Mads Pedersen (Trek-Segafredo), Cees Bol (DSM), Søren Kragh Andersen (DSM), Lasse Norman Hansen (Qhubeka-NextHash) and Edoardo Affini (Jumbo-Visma) are all riding too.
There were some crashes, as is to be expected on tight roads on an opening stage of a race, but one of the riders that was staying down was defending champion Niklas Larsen, who recently took silver in the men's team pursuit at Tokyo 2020 Olympic Games. Results at the time of writing do not confirm whether he was able to finish the stage.
Tour of Denmark 2021, stage one: Struer to Esbjerg (175.3km)
1. Dylan Groenewegen (Ned) Team Jumbo-Visma, in 3-55-36
2. Mark Cavendish (GBr) Deceuninck - Quick-Step
3. Giacomo Nizzolo (Ita) Qhubeka-NextHash, all at same time
4. Arvid de Kleijn (Ned) Rally Cycling, at 2 seconds
5. Cees Bol (Ned) Team DSM
6. Mike Teunissen (Ned) Team Jumbo-Visma
7. Mads Pedersen (Den) Trek-Segafredo
8. Tosh van der Sande (Bel) Lotto-Soudal
9. Jannik Steimle (Ger) Deceuninck - Quick-Step
10. Yves Lampaert (Bel) Deceuninck - Quick-Step, all at same time
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