A Bas Dost double took his Eredivisie tally to 30 for the season as Heerenveen moved into fourth place with a 4-2 victory away to Heracles Almelo.
Heerenveen also moved level on 61 points with AZ Alkmaar and Feyenoord in second and third, although they could slip back to sixth if FC Twente and PSV Eindhoven win their matches in hand on Monday (EST).
Heracles's own outside hopes of claiming a UEFA Europa League playoff place receded further with this defeat, while Heerenveen has now scored 11 times in winning its last three away league games.
Dost opened the scoring in the 13th minute and Luciano Narsingh
doubled their advantage 10 minutes into the second period.
Overtoom pulled one back with a penalty for Heracles, but Filip Djuricic
made it 3-1 with a well-taken effort.
Thomas Bruns cut the gap back to one but Dost finished what he had started with the sixth goal of the match 10 minutes from time.
Vitesse Arnhem remains seventh after a 3-2 win over bottom side Excelsior to extend its unbeaten run to five matches.
The visitor looked set to move above De Graafschap when an own goal from Jan-Arie van der Heijden and a Roland Alberg effort put them 2-0 in front.
But Alexander Buttner pulled one back from the penalty spot in
first-half injury time and, after Excelsior had Jordy van Deelen sent
off in the 75th minute, levelled with another penalty 10 minutes from
And worse was to come for the 10 men as Marco van Ginkel completed the Vitesse comeback two minutes into added time to condemn Excelsior to its sixth defeat in a row.
NAC Breda climbed into 14th place with a 3-1 win away to FC Utrecht, leapfrogging ADO Den Haag after it lost 2-1 at VVV-Venlo.
NAC had not won in six coming into this game and fell behind to a
Frank Demouge goal in the ninth minute.
But it stormed back to all but secure its top-flight status as first Robbert Schilder equalised with 18 minutes to go before Alex Schalk put it in front in the 89th minute and Jeffrey Sarpong added a third in injury time.
Third-bottom VVV's win over ADO ended a seven-game losing streak and brought it to within four points of its opponent, which occupies the final position of safety, with two games to play.
Barry Maguire gave VVV an early lead but ADO equalised when Kenneth
Omeruo headed home after a corner in the 19th minute.
Nigerian's evening went quickly downhill from there as he scored an own
goal three minutes later to restore VVV's lead and was then sent off in
the 69th minute for a second bookable offence.