The 26-year-old left at the end of last season, but made his first appearance of a second spell with the Highland club yesterday and added an obvious touch of class as Derek Adams' side claimed their first home win since early October, courtesy of Graham Carey's late strike.
Striker Jordan Slew, on loan from Blackburn Rovers, couldn't quite the repeat impressive impact he made in County's salutary Highland derby win over Inverness Caledonian Thistle four days earlier but still ensured a side that ended 2013 on a low of 10 successive games without victory carried much more menace.
Manager Adams also blooded on-loan Rotherham midfielder Michael Tidser late on and is vowing the three new faces will only be the start of his annual January squad upheaval.
"It's another very good victory for us. Over the 90 minutes we probably deserved it," Adams said. "The new signings are helping the players who were already here. The same happened last January and we've still to add further to the squad.
"We've been playing well but not getting the breaks or the results we deserved. We just had to keep knuckling down and working hard and that's what we've done. [The victories] are a psychological boost for us. We go above Partick, although they have a game tomorrow against Hearts."
County instantly looked a sharper, hungrier and more confident bunch than the rather bedraggled group that toiled to the end of 2013. St Johnstone had a new signing of their own on their bench in frontman Michael O'Halloran, released by Bolton Wanderers, and were looking to bounce back from a heavy defeat to Motherwell.
The hosts opened with a certain zip to their play, but it proved an even first half, with the visitors looking dangerous on the break.
Alex Cooper's teasing cross from the left was hacked over the bar by Steven Anderson and Nigel Hasselbaink might have released Stevie May behind the home defence, but his pass was just too heavy. Oikonomou was delighting the home crowd with some classy, confident touches and almost created the opener after 21 minutes.
The Greek's wonderful curling cross from deep left found Slew sneaking in at the far side of the box, but his bulleted header went just over.
Five minutes before the break. Ben Gordon fed the big English striker with his back to goal just outside the box. Slew's turn and strike were instant, but St Johnstone goalkeeper Alan Mannus tipped the ball from under his bar.
Hasselbaink immediately raced away on the counter and made good ground before Stuart Kettlewell bravely shut down May's blast.
As the second half started, Slew forced an immediate corner, but Saints broke again. Hasselbaink drove forward and slipped the ball to Chris Millar just inside the box but the midfielder's shot was just high and wide of the angle of bar and post. County pressured again and defender Brian McLean smacked a header just over.
Adams brought on Dutch attacker Melvin De Leeuw, with Saints blooding new signing O'Halloran soon afterwards.
Murray Davidson tested home goalkeeper Michael Fraser down low with four minutes left, but the County's moment was about to come. Richard Brittain released De Leeuw on the right and he showed strength to shoulder off the challenge of Frazer Wright before rolling a pass for Carey to blast high past the exposed Mannus from eight yards.
St Johnstone manager Tommy Wright said: "The game had 0-0 written all over it. It was always going to take a wonder goal or a mistake to win it - and that proved to be the case.
"At first I thought Frazer slipped because although the pitch looked magnificent it was quite slippy. But he just lacked that bit of concentration and their lad nicked it off him and it cost us.
"We should have come away with at least a point. We had a lot of good opportunities, but the final ball was poor and both defences did well."