He played the straight man to Bob Slavenburg, his mercurial partner, who died in 1981. Together they won the World Pairs Olympiad title in 1966 in Amsterdam and were second at the 1965 and 1966  European Teams Championships in Ostend, Belgium. Kreijns was also third on the Dutch team at the 1980 World Team Olympiad in Valkenburg, the Netherlands, with the partner Hans Vergoed.

In the 1980s Kreijns was the Dutch junior coach, his star pupils being Enri Leufkens and Berry Westra, who won the 1987 World Junior Team Championship and the 1993 Bermuda Bowl.

Kreijns captured 12 national titles and is still the greatest master-point winner in Dutch history.