Twente remain top with 44 points after 16 matches, two more then PSV Eindhoven who beat bottom side RKC Waalwijk 2-0.
John Goossens opened the scoring for Nijmegen after 15 minutes but goals from Kenneth Perez, Blaise Nkufo and Miroslav Stoch between the 18th and 31st minutes put Twente ahead.
Belgian Bjorn Vleminckx hit two goals in the last four minutes before the interval to bring NEC level but he was sent off early in the second half and Costa Rican Ruiz sealed Twente's 11th straight league win with a close-range header.
PSV struggled for an hour with lowly RKC before Balazs Dzsudzsak set up Jonathan Reis to break the deadlock and then connected with Danko Lazovic to put them 2-0 up.
Ajax Amsterdam fell further behind, on 35 points in third place, after a 2-0 defeat at Utrecht, while fourth-placed Feyenoord, on 31, came from behind to beat Groningen 3-1.
Ajax dominated the first half but failed to score and Jacob Mulenga put Utrecht ahead three minutes into the second half with a deflected shot before Jan Wuytens doubled the lead with a header.
Ajax finished with 10 men after a second booking in the 74th minute for Vurnon Anita.
Koen van der Laak gave Groningen the lead with an early goal but Feyenoord replied after the interval with Stefan Babovic, Roy Makaay and Jon Dahl Tomasson on target.
