AZ Alkmaar scored once in each half to inflict a comfortable 2-0 defeat on out-of-sorts Heerenveen.
The Europa League hopefuls went in front through Pontus Wernbloom after weathering early Heerenveen pressure.
The points were wrapped up midway through the second half when Hector Moreno tapped in from inside the box to rubber-stamp the win.
Groningen saw their European hopes dented with a 4-1 home defeat by Roda JC as Mads Junker scored a hat-trick for the visitors.
Junker had put Roda 3-0 up before Nicklas Pedersen hit a consolation with two minutes remaining.
There was still time for substitute Boldiszar Bodor to net a fourth for the visitors.
Excelsior won the relegation tussle 4-0 against bottom side Willem II but still remain the bottom three on goal difference.
Geert-Arend Roorda netted twice, one a penalty, and Excelsior’s other goals came from Nayib Lagouireh and Guyon Fernandez.