He plugged away over the last 30 kilometres of the 198.5km 11th leg from Le Bourg d'Oisans to finish 1min 26sec ahead of the sprint for second place.
As he raced along the Cours Fauriel finishing straight he looked around at his team car and gave a little punch of joy. It was an achievement for his Lampre team, who were reduced to five on Wednesday when four riders succumbed to the Alpine climbs, and a personal triumph for the lanky Dierckxsens, who only became a professional at 30 and is riding in his first Tour.
"It's a big dream," the 34-year-old said. "Two weeks after becoming Belgian champion I have won a Tour stage. Marvellous, incredible, fantastic. It has been a very hard day."
Not that he would have minded. Five years ago Dierckxsens was working in a factory spraying cars, and cycling was only a hobby until he discovered he had the talent for racing.
Neither the Belgian, who would have made his debut on the tour last year, but for a bad fall in which he broke his wrist, nor the rest of the leading group posed a threat to Lance Armstrong's overall lead. The American and his main rivals took a breather, finishing more than 22 minutes after Dierckxsens had crossed the line.
The Belgian joined a five-man chase after his compatriot Rik Verbrugghe had escaped more than 100km from St Etienne. They caught him and stretched the advantage until, on the 24km climb on the Col de la Croix de Chaubouret, Dierckxsens made his move.
Walter Godefroot, the last Belgian to win here in 1971, is now the team chief of Deutsche Telekom, so for him Dierckxsens victory extended a celebration. He had spent the day savouring Giuseppe Guerini's dramatic win for his team Wednesday win at l'Alpe d'Huez.
Yesterday Guerini came face to face again with the fan who, in trying to take his picture, ended up knocking him of his bike within a kilometre of victory. This time they shook hands, and 19-year-old Eric the Fan, as the amateur snapper has become known, apologised for his untimely intervention.
It has been a time for reconciliation. The Tour director, Jean-Marie Leblanc, shook hands with Richard Virenque, the rider he would have shaken by the throat before the Tour began. Two weeks before the off Leblanc wanted to bar Virenque for his alleged involvement in the continuing doping scandal, but the Union Cycliste Internationale invoked a rule that states bans must be announced a month ahead of a race.
Not that Leblanc could easily have avoided the Frenchman. Virenque has been a daily feature on the podium to receive the red polka-dot jersey for the best climber, which he has won four times in the past five years.
Claiming one of the specialist jerseys might be reward in itself, but money is a major motivator on the Tour, with 15m French francs (pounds 1.5m) to be won. Since the Tour began 12 days ago Chris Boardman's Credit Agricole team has have 261,850 Ffr, with Casino, whose Jaan Kirsipuu wore the yellow jersey for six days, a close second on 245,600Ffr.
Kirsipuu has departed after putting Estonia on the Tour map, and so too has Italy's Mario Cipollini after his historic four successive stage wins for Saeco, helping the team to 240,750Ffr.Reuse content