Celtic's tendency to do things the hard way almost came back to bite them at McDiarmid Park after the Parkhead side saw a commanding lead withered down once again.

Brendan Rodgers' side had raced into a 3-0 lead at the break following a performance that was full of vim and vigour with three good goals to boot. However, as they took their foot off the pedal in the second period St Johnstone forced their way back into it via a spot-kick from Danny Swanson before Steven MacLean nicked a late second.

Just as they did against Hapoel Be'er Sheva midweek, though, Celtic were able to re-assert themselves. Ryan Christie netted Celtic's fourth as the game drew to a close, restoring a sense of comfort to the Parkhead side.

However, there must be a worry about Celtic's continued ability to flirt with self-destruction, particularly in games where they ought to be out of sight.

On the first-half performance alone the Parkhead side were value money as their domestic bandwagon looked to gather pace.

Goals from Leigh Griffiths, Scott Sinclair and James Forrest meant that they were in a position to change the look and tempo of the side by resting players with a view to Tuesday night's game in Israel, a move that almost came back to haunt Celtic.

Griffiths, first to go to get his feet up, had marked his 26th birthday by netting the opening goal after decent work on the flank from Kieran Tierney. The striker, though, wouldn’t have been too happy with the card he collected shortly afterwards when he was booked by referee Craig Thomson for a perceived dive in the box.

Celtic, though, had little to gripe about. Scott Sinclair added a second, with Saints keeper Alan Mannus unlucky after blocking initial attempts by Forrest and Griffiths before the former Aston Villa midfielder added his third goal in four games after signing from the club a fortnight ago.

Forrest, unrecognisable from the fragmented player of recent season, netted a cracking solo effort when he waltzed forward before unleashing a shot into the bottom corner. It was game over by that point with Celtic content to wrap up the points and get their feet up ahead of this week's defining game in Israel.

Nir Bitton and Forrest were next off with Liam Henderson and Ryan Christie brought into the fray.

It took the pace the pace out of the game somewhat although Rogic saw one shot cannon off the crossbar as the game restarted.

St Johnstone, though, slowly tried to get themselves back into the match with David Wotherspoon's free-kick turned onto the bar by Craig Gordon, before the Hoops keeper had to pick the ball out of net. Danny Swanson was fouled by Henderson in the box before he dusted himself down and duly dispatched the spot-kick to give Saints a lifeline.

When MacLean pulled back a second, there were jitters within the Celtic defence. They were assuaged when Christie added a fourth to seal the points from the Parkhead side.