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.
Get the best features, fun and footballing frolics straight to your inbox every week.
Thank you for signing up to Four Four Two. You will receive a verification email shortly.
There was a problem. Please refresh the page and try again.