Neil Lennon shields the ball from Scott MacKenzie (TomShaw/Allsport)

He even managed to fluff his first few lines yesterday by wasting chances and then miscontrolling the ball when presented with a gift of an opportunity on 38 minutes.

But, within seconds,he regained his composure to score the goal which clinched championship glory for Celtic and ensured he will now never be forgotten.

As in the case of Harald Brattbakk three years ago when Wim Jansen's side were title winners on the last day, Parkhead had an unlikely goalscoring hero.

And, as with the Norwegian, Johnson - the man whose touch confirmed the return of Scotland's premier trophy to the east end of Glasgow - could be on his way out of the club.

He was substituted for Jackie McNamara early in the second half and was in tears as he sat in the dug-out to watch Celtic cling on, perhaps realising he had played his last major part for a team now chasing its first Treble since 1969.

Without him, Celtic played out the final, nervous 36 minutes to secure a slender victory. But that was only the sideshow to what the club and supporters had already decided was going to be a party day for all.

St Mirren had been in the market for all manner of exotic forwards from around the world with wage packets a club could quite conceivably die for.

What they needed yesterday, though, was a defensive performance from another planet to stop the side which was 20 goals more prolific than any other before kick-off.

Their success in holding out for so long was not through any title-day nerves from Celtic.

The home team's football flowed and they created shots on goal every three minutes of the first half as they showed a desire to get the job done quickly.

Rather, St Mirren's survival was by virtue of wasteful finishing by Johnson and a string of saves from Ludovic Roy.

Lubomir Moravcik was the magician conducting Celtic's forward play. He darted from left to right, suckered Saints players into tackles, went to ground, but always sprung back up to torment.

The Slovak's shuffle created chances aplenty for himself, one at the front post which Roy batted down for a corner, a fizzing drive from distance which was one of ten off-target from Celtic in the first half and a header sent bouncing across goal and inches wide.

The first serious opportunities came the way of, and were spurned by, Johnson. In 21 minutes, he scampered clear of St Mirren's defenders on to the outstanding Neil Lennon's through pass but couldn't find a way to guide the ball past Roy, whose sprint to block was an excellent piece of alert goalkeeping.

Johnson then scraped the paint of Roy's left-hand post after his cute penalty-box run matched Moravcik's pass and his shot on the turn flashed across the face of goal.

Barely half an hour had expired before Celtic's attempts to score looked a little desperate. Ramon Vega miskicked from ten yards and, after Didier Agathe destroyed poor Chris Kerr on the right, Jamie McGowan came within inches of diverting the ball into his own net.

More near things looked set to follow after 38 minutes when Johnson's poise and control deserted him in the penalty area after Larsson burst on to an Alan Thompson feed and set up the Englishman in total isolation.

He may have messed up at first, but he had time to gather the ball again and, with the St Mirren defence still in disarray, stroked a right-foot drive below the scrambling Roy and clear of the last-gasp slide by McGowan.

Relief enveloped the stadium and now warmed up, the crowd rubbed their hands at the prospect of a landslide victory to confirm a first term in office by Martin O'Neill of utter dominance.

But they were never able to pull away from St Mirren, the bottom side in the division but one of the few to escape a serious beating at Parkhead this season.

Tom Hendrie's boys did not enjoy any sustained pressure and only flirted with causing Rab Douglas any concern.

With more intelligence and unselfish play, St Mirren might have silenced the crowd of 60,440 crowd.

A long ball from Jose Quitongo sent Graham Fenton down the right on the counter-attack but he opted to crash an effort wide instead of seeking out the unmarked Steven McPhee in the area.

And what was Quitongo playing at when he couldn't resist trying to score the kind of goal only seen in computer games?

Having danced his way round three Celtic players, options opened up ahead of him but he ignored them all and ran into Johan Mjallby.

Substitutes Michael Renfurm nor Steven McGarry were able to make an impact in the second half. For, on the few breaks Hendrie's side managed, Lennon was there to sweep clear any danger.

His signing in December came at an important time for Celtic, his introduction seemless and performances since almost effortless.

He was in the right places at the right time when, after Joos Valgaeren went off injured, other Celtic defenders momentarily lost their way.

Earlier, Jackie McNamara had replaced match-winner Johnson and could have helped himself to some of the goalscoring glory.

Roy's point-blank save from the Scotland player was only matched by the St Mirren No 1's acrobatics to deny Agathe from 25 yards.

All that was missing to raise the roof and cap the perfect day for Celtic followers was some magic from Henrik Larsson. It hasn't been a big task all season but yesterday he failed to fire.

After Roy denied him twice in the first half and he arched a free-kick over the bar, Larsson flashed in front of Scott Walker eight yards from goal to meet Agathe's low cross.

With the goalkeeper stranded on his line, however, Larsson pushed the ball so narrowly wide of target.

St Mirren's 400-strong support could be heard briefly as 90 minutes expired and perhaps the realisation crept into Celtic minds that any slip-up would spoil the day.

But then came the din. Fourth official Garry Mitchell's signal of only one minute injury-time was the cue for all in green to stand to attention, the final whistle an alert to party and salute a remarkable Scottish Premier League season by Celtic.