Paul Sheerin opened the scoring for the Perth Saints in the 15th minute with a sweet 20 yard volley after Partick failed to clear a Peter MacDonald cross.
Patrick's sole effort of note in the first half came from Mark Roberts who did very well to hold off his marker and shoot which St Johnstone's goalkeeper, Bryn Halliwell saved at full length.
Kenny Arthur then produced his own top class save in the 27th minute from Sheerin's spectacular 25 yard blockbuster which the keeper just managed to deflect onto the post and wide.
Partick began the second half in better form and went close twice. First through a Roberts header in the 55th minute which was steered wide by Halliwell and then in the 58th minute Jim Gibson shot over from 15 yards.
The second goal came from former Rangers striker Peter MacDonald in the 73rd minute. An excellent through ball from Martin Hardie meant the striker didn't need to take a touch before lashing the ball past Arthur to make it 2-0 and secure the points.