After the Olympic Games, Karstens started a successful professional career, where he won six stages in the Tour de France, 14 stages in the Vuelta a España, 1 stage in the Giro d'Italia, and other races such as Paris–Tours and GP Fourmies. He became Dutch national road race champion in 1966.
In the 1974 Tour de France, Karstens finished second in the fourth stage. Afterwards, he forgot to take the doping tests. The tour organisation set him back to the last place of the stage results, and gave him 10 minutes penalty time in the overall classification, which made him lose his third place.[2] One day later, the jury took the penalty time back. Thanks to 5 seconds of bonification that Karstens won during intermediate sprints, he took over the yellow jersey from Eddy Merckx.[3] He wore yellow for one stage before losing it to Patrick Sercu after stage 6A, but he reclaimed the overall lead after stage 6B to spend another stage in Yellow before Merckx took over the lead for the remainder of the Tour.
Karstens died of complications from a stroke on 8 October 2022, at the age of 80.[4]
Major results
1962
Ronde van Limburg
1964
Ronde van Noord-Holland
Ronde van Overijssel
Gold medal 100 km team time trial 1964 Olympic Games
