Ismael Bouzid, Ian Black and SusoSantana all missed out through suspension, but captain Michael Stewart took his place in the middle of the field after winning an appeal against his dismissal.
Obua passed up an excellent chance to put the ball in the net when his attempted tap-in was blocked by Fraser, but the Hearts man had already been flagged offside shortly before Suso Santana's volley was saved by the Motherwell keeper.