Hyung-jun Suk scored twice as Eredivisie leaders PSV Eindhoven were comprehensively beaten 3-0 by mid-table FC Groningen.
PSV were victorious in their midweek Europa League trip to Trabzonspor but returned to domestic action with a bump.
Suk opened the scoring after 29 minutes and Leandro Bacuna added a second in the 51st minute before PSV had Stanislav Manoleve sent off for a second yellow card and Suk netted again before the close.
AZ Alkmaar were unable to capitalise on PSV's shock defeat as they too crashed to an unexpected loss, going down 3-0 at relegation-threatened FC Utrecht.
AZ could have gone three points clear at the summit following PSV's 3-0 defeat at mid-table FC Groningen but Gertjan Verbeek's side slumped to an identical loss at Utrecht following a nightmare first half.
Utrecht took the lead in the 14th minute through an Alexander Gerndt penalty in an incident that also saw AZ reduced to 10 men when Niklas Moisander was sent off.
Utrecht then took full advantage of their numerical superiority to add a second goal through Gerndt six minutes later before Edouard Duplan made it 3-0 just before half-time. There was no way back for AZ after that as they slumped to only a fifth Eredivisie loss of the season.
FC Twente maintained their title push with a commanding 4-1 win at Vitesse Arnhem.
Steve McClaren's men took control with goals from Leroy Fer, Luuk de Jong and Ola John before their goalkeeper Peter Wiesgerhof was sent off 10 minutes from time.
However, Wilfried Bony was unable to take advantage of the resulting penalty and a bad day for the home side was compounded in the 83rd minute when Nacer Chadli made it 4-0, before Mike Havenaar's late consolation for Vitesse.
An irresistible first half from Ajax saw them to a comfortable 4-1 victory over NEC Nijmegen and moved them to sixth in the table.
The home side showed no ill effects from their midweek defeat to Manchester United in the Champions League, with Dmitri Bulykin opening the scoring in the fifth minute. Jan Vertonghen added a second in the eighth minute before Bulykin scored again before half an hour had been played.
The second half was more even, with Ajax scoring a fourth through Siem de Jong and NEC finally getting something to cheer when Rens van Eijden headed home from close range.