Kevin James and Stephen Dobbie tested Hamilton early in the match, but it was not until half-time that the game burst into life.
The superb Jason Scotland embarked on a surging run down the right before cutting the ball back to Simon Mensing. The defender displayed to all present why he was required to play in defence as the Englishman blasted the ball over the bar from 10 yards when he should have scored.
Hamilton immediately broke and almost scored when Mark Gilhaney's cross was turned towards goal by Brown Ferguson. Goalkeeper Matt Glennon completely went the wrong way but managed to extend a toe to deflect the ball past the post.
Back down the other end the play swung and from a Paul Sheerin corner the Saints took the lead. The towering skipper of the Perth side, Kevin James, barged three defenders out of the way as he rose to head his side into the lead. despite Alex Neil trying his best to keep the effort from crossing the line.
The away side doubled their lead in the 72nd minute when Dobbie slid a perfect through ball to Scotland. The Trinidad and Tobago star had plenty of time to tuck his effort into the top corner.
Hamilton, to their credit, did not succumb easily and battled back into the match almost immediately. An Alex Neil corner found Scott Tunbridge unmarked the near post, and the striker flicked the ball into the net.
Hamilton pressed for an equaliser but could not find their way past a solid St Johnstone rearguard.
The Saints are now only one point behind second placed Ross County, but Hamilton have slipped to fifth in the league.