Tomasson goal fires Feyenoord past RKC
A lacklustre Feyenoord had a poor first half but improved directly after the break when Tomasson scored with a fine volley.
Feyenoord finished with 10 men after Denny Landzaat was sent off six minutes before time.
PSV Eindhoven, 2-1 winners against Utrecht on Wednesday, are top with 55 points after 21 matches, ahead on goal difference of Twente Enschede, who beat neighbours Heracles Almelo 2-0.
Steve McClaren's Twente will travel to third-placed Ajax Amsterdam (46) on Sunday.
Feyenoord remain fourth with 42 points.