Maarten Martens struck twice in three second-half minutes as AZ Alkmaar beat Excelsior 2-0 to go three points clear at the top of the Eredivisie table.
After AZ dominated the first half, Martens gave his side a deserved lead 13 minutes after the break. The Belgium international then added a second soon after to confirm a win that took AZ to the top, for 24 hours at least, with second-placed PSV Eindhoven hosting De Graafschap on Sunday.
Ajax will still hope to have a say in the title battle, although they remain well off the pace in sixth place, eight points behind AZ, despite a 2-0 win at NAC Breda.
Dmitri Bulykin put Ajax ahead in the 68th minute and substitute Nicolas Lodeiro wrapped up the points with a minute remaining.
Further down the table, Roda JC beat NEC Nijmegen 1-0 with a 56th-minute goal from Sanharib Malki, to climb one place to eighth.
Roda climbed above FC Groningen who slumped to a 2-0 defeat away to VVV-Venlo. Yanic Wildschut and Uche Nwofor scored in the opening half-hour as VVV, bottom at the start of the day, climbed two places to reach 16th in the table, leaving De Graafschap at the foot of the league.