Heerenveen and Vitesse picked up victories against Feyenoord and PEC Zwolle in the first legs of their Eredivisie play-off games for UEFA Europa League qualification.
Swedish midfielder Simon Thern was Heerenveen's hero, heading home Henk Veerman's knock-down from close range in the 83rd minute as Feyenoord appealed in vain for offside.
Feyenoord are now six games without a win, and a failure to beat Dwight Lodeweges' in the regular season will do little to boost the Rotterdam club's spirits ahead of the second leg at De Kuip.
Vitesse will defend their advantage on home soil, having come from behind to beat Zwolle 2-1.
Maikel van der Werff will join Vitesse at the end of the season, but his loyalties remain with Zwolle for now and he put them ahead midway through the first half.
However, the visitors came out strongly in the second half and turned the tie on its head thanks to goals from Marko Vejinovic and Valeri Qazaaishvili.
The second legs of both ties will be played on Sunday.
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