He ran in the Marathon at the 1991 World Championships in Tokyo, finishing in 16th place with a time of 2:22:17. That year he also competed in the IAAF World Cross Country Championships, but he only managed to finish in 29th position. The following year he competed at the 1992 Summer Olympics, but he did not finish in the Olympic Marathon race. At the Amsterdam Marathon in 1993, he took second behind Kenichi Suzuki with a time of 2:12:27. He was highly successful at the Warandeloop cross country race: he won in 1984, 1985, 1988, 1990, and 1993, making him the runner with the most titles ever won at the competition. He was also a seven-time national cross country champion; only Kamiel Maase and pre-war competitor Jan Zeegers have more wins than Dirks. He won the Eurocross meeting in neighbouring Luxembourg in 1991.
Further success came in road running competitions in the Netherlands: he won the Zevenheuvelenloop 15-kilometre race three times consecutively from 1989–1991, setting a course record which was beaten by Haile Gebrselassie after five years. He won the Egmond Half Marathon in 1991, and was twice victorious at the Parelloop race (in 1991 and 1993). He was also the 1992 champion of the Bredase Singelloop hardloopteam. At the Paderborner Osterlauf Half Marathon in Germany, Dirks took first place 1989 and again 1991.