Eight straight wins for Twente in Holland
Ruiz (pictured) headed a free-kick from Theo Janssen into the net early in the second half.
Twente remain top with 35 points after 13 matches, two more then PSV Eindhoven who brushed aside nine-men ADO Den Haag with a 5-1 away win. Ricky van den Bergh and Lex Immers were both sent off.
Swede Ola Toivonen settled the match with a first half hat-trick and added his fourth to complete the rout.
Sekou Cisse's sixth-minute goal gave Feyenoord an early lead at AZ Alkmaar before Brett Holman salvaged a point for the defending champions.
Feyenoord remain fourth with 24 points, five behind Ajax.