By Mark Buckingham
Last Updated: 01/01/70 1:00am
Ronald Koeman's men followed up the midweek 4-1 reverse at Heerenveen with a 1-0 loss at Utrecht.
Stefaan Tanghe grabbed the only goal of a disappointing contest on 76 minutes with Ajax unable to muster a response.
The visitors were a subdued force with Yannis Anastasiou unable to find his sights in front of goal before being substituted.
Rafael van der Vaart had a shot saved by Joost Terol before Tanghe struck the winner to check Ajax's momentum at the top of the table.
PSV failed to take advantage of Ajax's defeat as they slipped to a surprise loss at home to Roda JC.
Aroune Kone and Cristiano had Roda JC ahead inside 20 minutes and though Jan Vennegoor of Hesselink pulled one back, PSV could not conjure an equaliser.
Feyenoord produced a fine performance in the closing half hour to beat Willem II Tilburg 3-0 away from home.
Half time substitute Anthony Lurling broke the deadlock on 60 minutes and Song Chong-gug and Ebi Smolarek wrapped up the points for the visitors.
ADO Den Haag boosted their survival prospects with a vital win at fellow relegation strugglers Volendam.
Cedric van der Gun opened the scoring on 50 minutes and Roy Stroeve's 87th minute effort sealed the success.
RKC Waalwijk remain firmly settled in mid-table after holding on for a 2-1 triumph at Groningen.
Substitute Jason Oost opened the scoring midway through the second half and Yuri Cornelisse made it two ten minutes later. Regillio Vrede reduced the arrears for the hosts but it proved no more than a consolation.