Chris Sutton pushed Celtic back to within three points of league leaders Rangers with a first-half double at Firhill.
Sutton, partnering Henrik Larsson up front in the absence of John Hartson, punished Partick Thistle for slack defending with two opportunist strikes.
His first came after just seven minutes and it left the Jags chasing a game that always looked to be drifting away from them.
He bundled home a shot from Jackie McNamara from close range with the Partick defence claiming offside, for his 14th goal of the season and his 15th followed shortly before half time.
Partick hit back after the loss of the early goal and Magnus Hedman had to spread himself to clutch a stinging shot from David Rowson.
Midway through the first half, Hedman had to look lively again to save a shot from Alan Archibald following a short free-kick from Alex Burns.
But Sutton struck again after 32 minutes when he punished a sloppy clearance from David Lilley to send a shot beyond Kenny Arthur.
Celtic were in cruise-control after that and Larsson was inches away from a third goal ten minutes from the break when he curled a 25-yard free-kick just past the post.
The champions had chances to add to their lead early in the second half with Larsson shooting straight at Arthur and then Sutton scooping a shot over the crossbar.
But Kenny Milne was desperately unlucky not to pull a goal back in the 58th minute when he lobbed the ball over Hedman, but was marginally too high and the ball found only the top of the net.
Burns then had an opportunity after 71 minutes, but his effort was comfortably saved by the alert Hedman.
Sutton had a chance to complete his hat-trick 12 minutes from time, but he shot wildly over the crossbar with only Arthur to beat.