Second-placed PSV Eindhoven beat visitors Vitesse Arnhem 1-0 to remain two points off the pace on 30 after 12 matches.
Twente's Slovakian Stoch set up Ruiz 11 minutes before the break to open the scoring with a fine chip and doubled the lead himself six minutes later with a deflected shot.
Jeanvion Yulu Matondo pulled one back for the home side early in the second half but they could not find an equaliser.
PSV's Balazs Dzsudzsak scored after a mistake by Vitesse keeper Piet Velthuizen in the 64th minute for their victory. PSV are now unbeaten in 19 matches in all competitions this season.
Lowly Heerenveen claimed a third league win of the campaign by beating 10-man ADO Den Haag 3-0. Roy Beerens opened the scoring before Michal Papadopoulos hit a double after the break.
Den Haag's Pascal Bosschaart was sent off just before halftime after receiving a second yellow card.
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