Ross County 4 St. Johnstone 0
County had the first effort on goal in the second minute, but Mark McCulloch blasted his effort over the crossbar from the edge of the box.
The home side looked in the mood and John Rankin set up Don Cowie with an opening, but Saints keeper Kevin Cuthbert touched the ball behind for a corner.
At the other end Colin Stewart was forced to punch a Peter MacDonald snap-shot clear, then the County keeper did well to block a low drive from Ryan McCann.
But it was mostly County and they deservedly took the lead in the 14th minute when Cowie linked up with David Winter and the former Dundee United striker scored at the second attempt after his initial shot was blocked on the line by Ian Maxwell.
It was constant pressure from the home side and a fine run down the left from Sean Kilgannon produced a second goal three minutes later.
The former Par got to the goal line and whipped the ball in for Winters to steer home at the near post.
The Saints were not entirely out of it, and after former County favourite Sean Webb sent in a lob that Stewart had to tip over, Kieran McAnsespie curled in a fierce free- kick that was just too high to cause Stewart a problem.
But County stormed back and scored again in the 34th minute when Martin Canning rose above the Saints defence in the six-yard box to head home a perfectly-flighted Kilgannon free-kick.
County almost snatched a fourth goal in the 48th minute when an ambitious lob from John Robertson was tipped over the bar by Cuthbert for the first corner of the second half.
Saints hit back and Stewart had to scramble the ball away on a couple of occasions. The visitors brought on Kevin Rutkiewicz and Michael Moore, but the County defence were dealing with all the Saints could throw at them.
County added to their lead in the 81st minute when a long-range shot from Rankin was parried by Cuthbert and Jim Lauchlan stepped in to slot the ball home.