Their five-game unbeaten run ended by Motherwell last week, the Pittodrie kids were determined to end the season on a positive note. The Saints have had a poor season, sitting third from the foot of the table, but Alan Maybury?s side did beat Kilmarnock last week so would have a spring in their step as they face Paul Sheerin's boys.
Experienced campaigners Greg Halford and Stephen Gleeson were in the home ranks while Saints had a team of teenagers on duty.
Miko Virtanen headed Chris Antoniazzi's free kick just over as the Dons made a positive start on a bitterly cold afternoon. Greg Halford forced a fine save from Sinclair in the sixth minute following a corner then the Saints goal was under onslaught as first Dangana, then Halford were denied by last-ditch clearances.
Ethan Ross was next to have a pop at goal after Antoniazzi's free kick was deflected out to him on the edge of the area, the shot flying wide. The opening quarter of an hour had seen Aberdeen dominate without anything to show for their efforts.
Sinclair was called into action again on 21 minutes, saving well at his near post from Dangana after Virtanen had nodded Halford's long throw into the striker's path. A rare Saints attack saw McKenzie play a dangerous ball into the Aberdeen box, but Lloyd Robertson was well positioned to clear. Shortly after skipper Jack Mackenzie did well to block a powerful shot from Brian as the Perth side grew into the game.
Great link-up play between Ethan Ross and Antoniazzi saw the latter race into the area only to be bundled over before he could pull the trigger, but loud shouts for a penalty fell on deaf ears.
Saints thought they had snatched the lead on 32 minutes when Northcott headed a fine Munro cross past Craddock, but their joy was short-lived as the flag was up for offside.
The deadlock was broken on 34 minutes.
Sinclair saved brilliantly from first Seb Ross, then Dangana, but was helpless as Virtanen placed a delightful shot from the edge of the area into his bottom corner. An excellent goal from the Finnish youngster, his third League goal of the season.
Despite more home pressure, Saints' defence stood firm to the reach the interval only one goal behind.
Half time - Aberdeen Reserves 1 St Johnstone Reserves 0
Saints made a change at the interval, Jack Wills replacing Sinclair in goal. Aberdeen doubled their advantage after only a minute of the second half, Seb Ross heading home Jack Mackenzie's cross from the left. Another well-worked goal from the Dons and good to see Seb back on the score-sheet.
Great work between Ethan Ross and Antoniazzi created an opening for Seb Ross but the older of the two brothers was denied by Wills when he really should have made it three.
Munro was booked on the hour mark after a crude foul on Ethan Ross, then Saints coach Alan Maybury made a second change introducing Hamilton for Green. Miko Virtanen missed a golden opportunity to notch his second of the game, heading over after some excellent build-up play.
Aberdeen were playing some great football but were guilty of missing chances. And Saints almost made them pay as Nethercott and Hamilton both missed opportunities to reduce the deficit.
Stephen Gleeson was instrumental in much of Aberdeen's good play, always looking for the ball and keeping things ticking over. Wilson of Saints was cautioned for a foul on Seb Ross.
Aberdeen went three upon 70 minutes, Miko Virtanen getting a well-deserved second goal as knocked home the rebound after Wills had parried an Antoniazzi effort. A third booking of the game went to St Johnstone's McKenzie after a foul on Antoniazzi.
Brian got one back for Saints on 74, just before Seb Ross and Antoniazzi were replaced by Max Barry and Lewis Duncan. Full back Brian was booked in 79 minutes for a trip on Ethan Ross then Ryan Harrington came on for Robertson.
Sub Max Barry tried his luck from distance as the clock ticked down towards 90 minutes, his shot arcing well wide of the keeper's right post. Luke Turner burst forward to have an effort on goal, but again Wills wasn't forced into a save.
A good, solid performance from Aberdeen who were not flattered by the scoreline in a game where both sides played some entertaining football.