St Mirren 0-2 Celtic

• Celtic move eight points clear at top

• James Forrest finishes Adam Matthew cut-back

• Stefan Johansen penalty after Viktor Genev hand ball

• St Mirren four points adrift at bottom

Celtic showed the poise and patience of champions as they overcame St Mirren to move eight points clear at the top of the Scottish Premiership.

The home side defended deep and in numbers, and were spirited at times.

A clever James Forrest goal and a Stefan Johansen penalty secured the victory for Celtic, who won without being at their most commanding.

St Mirren, who are focused on survival, could only take heart from moments of optimism scattered through the game.

And, despite at times giving Celtic a scare, they remain four points adrift at the bottom of the league.

The home side set out to stand their ground, denying Celtic the space and time in which to express themselves. The immediate challenge for Saints was to deal with the drifting menace of Kris Commons.

By dropping into pockets of space, Commons was a conundrum to St Mirren, since the defensive midfielder, Jim Goodwin, sat in front of the back four rather than follow him around the field.

There was not relentless pressure from the visitors, but Commons' interventions tended to be inventive.

On one occasion, he twice befuddled Marc McAusland before also trying to fool the goalkeeper Mark Ridgers by shaping to cross from the left but then rifling a shot towards the near post. Ridgers was agile enough to dive and save the effort, though.

After sending another effort into the side-netting and drawing a second smart save from Ridgers, Commons turned provider.

From his quick free-kick, the ball was worked upfield then back to Commons, who slipped a pass into the path of Forrest. His low shot from distance brought another fine save.

St Mirren were not overwhelmed, though, and occasionally found themselves able to push the Celtic defence back. Stephen Mallan and John McGinn were composed in central midfield, while James Dayton and Kieran Sadlier were intermittently bright out wide.

James Forrest (grounded) watches his shot hit the net to give Celtic the lead

The latter delivered a dangerous cross after being fed the ball by Jeroen Tesselaar, which Mallan met with a header, but there was not enough power or direction to trouble the Celtic goalkeeper Craig Gordon.

For all that these two sides had not seemed evenly matched, there was a spirit to St Mirren that suggests they will make a fight of the relegation battle until the end of the season. Celtic could afford to be more poised, since they could believe that their greater quality would eventually tell.

The teams traded chances in the second half, with Stokes snapping a shot on target that Ridgers held, while Mallan drove wide when the ball fell to him 25 yards out.

St Mirren had to be resourceful, since they were not good enough to submit Celtic to periods of pressure, while the visitors were able to command the ball in their opponents' half.

That eventually proved telling when they used precise, close-quarters passing to spring Commons down the inside right channel and his cutback was crisply steered into the net by Forrest.

St Mirren would have felt deflated, but there was also a moment of grievance.

When Forrest, having been enlivened by the goal, struck another effort on target, the ball spun off the hand of Victor Genev. The defender claimed that the contact was accidental, but the referee Alan Muir pointed to the spot.

Johansen converted the penalty with calm assurance, in keeping with the temperament of Celtic's play.

This was not a dismantling of St Mirren, who showed an element of resolve, but it was the kind of display and result that underpins a side's progress towards the title.