Mertens hits four in PSV pummelling
Ajax grabbed an early lead on the counter-attack when Derk Boerrigter set up scorer Miralem Sulejmani in the 10th minute.
The home side dominated for an hour but Twente then carved out their best chance, Denny Landzaat almost scoring with a close-range header.
De Jong then struck three minutes from time to give Twente 16 points from seven matches, one ahead of AZ Alkmaar and Ajax.
Mertens, the league's leading scorer, took his goal tally for the season to 11 to inspire PSV against Roda who were reduced to 10 men after 19 minutes following a professional foul from Jagos Vukovic.
Ola Toivonen, Kevin Strootman and Tim Matavz were also on target. Sanharib Malki replied for Roda.