Mitchell te Vrede opened the scoring for Heerenveen after 52 minutes having been teed up by a long pass from Sam Larsson, but the lead lasted only three minutes before Luuk de Jong equalised with his 19th league goal of the season.
The champions, who were jeered by their own fans after a goalless first half, could not find a winner and are now only two points ahead of Ajax, who will replace them at the summit if they win at home to NEC Nijmegen on Sunday.
With Heerenveen having won just one of their previous five outings, PSV had been heavy favourites and were hoping for a morale-boosting result ahead of their Champions League trip to Spain to play Atletico Madrid on Tuesday.
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AZ Alkmaar's Vincent Janssen scored for a sixth successive game and took his season's tally to 19 with two second-half goals in a 2-0 win at Willem II Tilburg that moved them clear in third place on 46 points.
Twente Enschede, who were second from bottom at the winter break but are now settled in mid-table, won for a sixth time in their last seven games as they came from a goal down to beat PEC Zwolle 2-1.
(Reporting by Mark Gleeson; Editing by Toby Davis)
