Randolph provided 23 points and 13 rebounds, helping boost Memphis to a third straight win.
Mike Conley chipped in 19 points and seven assists.
Marc Gasol netted 12 points and grabbed four rebounds in his return following a 23-game injury absence (sprained knee ligament).
The Thunder dropped a third straight road game despite 37 points from Kevin Durant.
Reggie Jackson added 17 points for Oklahoma City.