But Guyon Fernandez equalised in the 35th minute to secure the draw which means Ajax move to 48 points, still comfortably ahead of Twente Enschede, Feyenoord and Vitesse, all on 43.
"I'm sick about drawing this game which on the basis of how we played in the first half should not have happened. I still get surprised at how much we can slip off the pace but that shouldn't happen if you play for Ajax," said coach Frank de Boer.
Albert Finnbogason scored his 21st league goal of the season as Heerenveen bounced back from a midweek setback at home to Twente to beat FC Groningen 3-1 away.
Heerenveen's goals came in a seven-minute spell in the first half as Rajiv van la Parra and then Hakim Ziyech scored before Finnbogason converted a 40th-minute penalty after Maikel Kieftenbeld deliberately handled the ball to stop it going into the net and was red carded.
Groningen had a consolation penalty of their own late in the game converted by Michael de Leeuw.
RKC Waalwijk scored four goals in the last 11 minutes to thrash FC Utrecht 5-2 and continue their climb away from relegation danger.
(Reporting by Mark Gleeson; Editing by Rex Gowar)
