The unlucky Ramos deflected a shot from Christian Eriksen three minute before the break. Ajax failed to make it 2-0 when Miralem Sulejmani had a penalty saved in the 65th minute after Sigourney Bandjar had been sent off.
AZ Alkmaar remain top with 38 points after 16 matches following their 4-0 win over Graafschap Doetinchem on Saturday. They are four points ahead of PSV Eindhoven, 1-0 winners against NAC Breda.
Ajax are fourth with 30 points, while Feyenoord slipped to sixth with 28 after being held to a 2-2 draw by 10-man Utrecht.
John Guidetti scored his eighth goal this season to put Feyenoord ahead after 94 seconds but after 31 minutes Daan Bovenberg headed home the equaliser.
Soon after half-time, Edouard Duplan scored to earn Utrecht the lead but midway through the second half Jerson Cabral came in from the right to salvage a draw for Ronald Koeman's men.
At the bottom, VVV Venlo registered their second win of the season beating neighbours Roda JC Kerkrade 2-0 to move into 17th place with 10 points leaving Excelsior Rotterdam in the bottom spot with eight points.
Barry Maguire converted a penalty on the stroke of halftime after keeper Pawel Kieszek was sent off for a foul.
Seven minutes before time, after Mads Junker had missed a penalty for Roda, Ahmed Musa set up Bryan Linssen to double the lead.
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