It was a game of two halves in Perth, the Dons producing a much better performance after the break to secure a 1-0 win and close the gap on Hibs to four points.
Paul Sheerin made two changes to the team that beat Dumbarton 1-0 in the Scottish Cup last weekend. Jack MacKenzie returned to the side after being cup-tied, along with Matty Kennedy. Calvin Ramsay and Ethan Ross made way and started from the bench, as did the returning Fraser Hornby. On loan Callum Hendry missed out as he was not eligible to play against his parent club.
There were four changes from the St Johnstone side that won 1-0 in their Scottish Cup tie at Dundee. In came Craig Bryson, Glenn Middleton, Chris Kane and Craig Conway, replacing Liam Craig, David Wotherspoon, Guy Melamed and Stevie May who all dropped to the bench.
A quick break from the hosts put Aberdeen under pressure in the third minute, Tommie Hoban getting an important block on a Middleton shot to avert the danger. Two minutes later, Dean Campbell tracked back brilliantly to take the ball off Conway as he looked to be clean through on goal.
Kane then put Joe Lewis under pressure in the ninth minute as he had the ball at his feet but he was able to scramble the ball away. It was a high octane start from the Saints and in the 12th minute, Kane blazed over the bar from 10 yards out when it looked easier to score following a free-kick.
Gradually though the Dons played themselves back into the game, despite Andrew Considine collecting a yellow card in the 23rd minute to bring a Saints counter-attack to an end.
Aberdeen's first corner was won in the 25th minute, Niall McGinn delivering it onto Hoban?s head, but a deflection helped take it wide of goal. Kerr had a similar chance from a 33rd minute corner at the other end but he put his header wide too.
HALF-TIME: ST JOHNSTONE 0 ABERDEEN 0
At the break, Hornby replaced Flo Kamberi as the Dons looked for the ball to stick better up front. Three minutes in, a McGinn corner caused trouble, Clark clawing the ball away under the bar. Recycling the ball, McGinn speared it into the near post, just in front of Hornby.
The positive start to the half was continued when Jonny Hayes slotted the Dons into the lead on 52 minutes. Kennedy played a neat through ball through the middle, Hayes accelerating away from two defenders and maintaining his composure in the box to poke the ball past Clark and in.
McGinn was the second man in the book as Saints tried to break on Aberdeen on the hour, but it was much better from the Dons in the second period, pushing Saints back into their own territory. It should have been 2-0 in the 68th minute, good play from Aberdeen down the right culminating in McGinn standing up a cross to the back post where Hornby put his header into the side netting, a great chance.
May and Wotherspoon replaced Middleton and Kane in the 70th minute, a measure of the Dons? control of the game, Saints desperately looking to change the direction of things. Aberdeen responded, bringing on Ramsay and Connor McLennan for Kennedy and McGinn in the 76th minute.
It was Saints who had the next opportunity in front of goal, May helping on a cross to Rooney at the back post. He got in front of MacKenzie and Hayes to win a good header but fortunately, it smacked against the post and bounced away to safety. Melamed and Tanser then joined the fray in the 79th minute, Bryson and Booth replaced.
Rooney caused problems again as Saints rallied in the 80th minute, dashing into the box at inside-right, squaring the ball into the six-yard box, Hoban stretching to clear in front of May. O?Halloran then became the final change for the hosts, on instead of Conway.
Lewis kept his side in front with a terrific save in the 89th minute, prolonged Saints pressure seeing the ball fall kindly at the feet of McCann. The. Goal was gaping for him on the edge of the six-yard box but Lewis flung himself to his right to keep the clean sheet intact and to see his side through to a vital victory, Ross replacing Hayes to run the clock down in the 93rd minute.