The St Johnstone striker's highly contentious 73rd-minute goal, which Celtic claimed had not crossed the line, was the vital margin of difference. Celtic had no such fortune. Their substitute, Harald Brattbakk, watched Saints' Philip Scott clear his net-bound effort off the line in injury time.
Celtic were forced to play without their top scorer, Henrik Larsson, who was unfit with a hamstring injury but even the Swedish international's absence could not help new pounds 2m signing Brattbakk find a place in the side. Instead, coach Wim Jansen elected to use Darren Jackson instead.
St Johnstone had Alan Kernaghan back in their defence, just days after thinking they had lost their Irish defender, whose three-month loan spell in Perth ended last week. However, Kernaghan has persuaded Manchester City's chairman Francis Lee to let him remain in Scotland until the end of the season.
O'Boyle came closest to opening the scoring after just five minutes. The Northern Ireland striker got free of his marker, Enrico Annoni, but Celtic goalkeeper Jonathon Gould managed to smother the fierce right-foot shot.
That was the signal for a sustained period of St Johnstone pressure. Midfielder Nick Dasovic unleashed a stunning shot that was unfortunate to just elude the target and then, in the 14th minute, Dasovic and O'Boyle combined to put the latter clear of the pedestrian Annoni. O'Boyle got to the goal-line and should have picked out the incoming Allan Preston after luring Gould away from his goal, but the keeper made a vital intervention to rescue Celtic.
Gould's counterpart, Alan Main, cast off his inactivity soon afterwards by getting down at the feet of Morten Wieghorst to stop the Celtic midfielder's well-timed run from punishing St Johnstone.
St Johnstone may have lost all three preceding games to Celtic this season, two in the Premier League and a Coca-Cola Cup tie, but they were far from inhibited. That attitude was summed up when full-back Callum Davidson delivered a fierce 30- yard drive which brought out a wonderful save from Gould in the 34th minute.
Undaunted, Main matched that four minutes later by reaching backwards to stop Jackie McNamara's header from looping over him. St Johnstone central defender Jim Weir was booked soon afterwards for chopping down Tom Boyd. And from the free-kick Wieghorst's header was thumped off the line by Kernaghan.
As if reminded of the urgent need of a win to maintain their title ambitions, Celtic used the second half to up the tempo in their approach, but their moves lacked the vital cutting edge.
St Johnstone secured the points when Preston's corner was met by the upraised boot of O'Boyle and although Celtic claimed that David Hannah had cleared the ball off the line, a television replay later showed that the ball was indeed over .Reuse content