Dundee United tried to park the proverbial bus at Parkhead but got stuck in reverse gear as Celtic drove away with a resounding win.
The Tangerines, who now languish five points adrift at the bottom of the Premiership and have a minus 17 goal difference, adopted a damage limitation strategy against the Hoops but the problem was that it only lasted 23 minutes.
After that the Celtic goals came thick and fast and there was nothing the Tannadice men could do about it.
Leigh Griffiths opened the scoring, nipping in to shoot home from an acute angle after some dreadful dithering from United.
Dedryck Boyata headed home the second on 40 minutes then it was three in first-half stoppage time after Kris Commons scored a penalty that was conceded by Scott Fraser.
Commons added another on 54 minutes with a fine strike before home skipper Scott Brown rounded it all off in the final minute with a shot that deflected in off United’s Aaron Kuhl.
The Tangerines made just one change from the side that lost to Hearts and it was an enforced one.
Out went the suspended Blair Spittal after his red card and in from the start came Charlie Telfer.
United kicked off in a 4-5-1 formation, with Billy Mckay in attack.
The big news for the Hoops was that manager Ronny Deila named Commons in his team despite the midfielder’s tantrum in Molde in midweek. Indeed, Commons got a big cheer from the home supporters when his name was read out.
There were two former Tannadice men in the home line-up Stuart Armstrong and Gary Mackay-Steven and a third man, Nadir Ciftci, sat on the bench.
Of course, Celtic Park has not been a happy hunting ground for United, with their last win here coming back on December 26, 1992.
With some bookies offering odds as long as 20-1 before kick-off for an away victory there weren’t many spectators inside the stadium expecting anything other than a straightforward success for the Hoops and so it turned out.
Mackay-Steven and Armstrong linked up for the hosts on six minutes, with the former finding the latter in space at the back post but the shot was deflected over the United bar.
It was all Celtic early on and, after a rare United foray upfield, the home team came forward again and Armstrong’s shot from outside the box was pushed around the post by keeper Luis Zwick.
United had held out well…until the 23rd minute.
It was brilliant opportunism from Griffiths but terrible defending from the Tangerines.
With 11 men in around their own box, United still let a Brown pass work its way through and keeper Zwick was slow to react.
The young German had looked favourite to reach it but in nipped the ex-Dundee striker to move to the right then clip the ball home from the tightest of angles.
United tried to hit back quickly and John Rankin got a shot in after the ball was squared to him by Mckay but the ball flew over the bar.
Zwick did well to hold on to a Griffiths snap-shot as Celtic continued to camp in United’s half but the defensive dam was breached for a second time on 40 minutes.
After Kieran Tierney was fouled on the left wing, Armstrong sent the freekick over and Boyata jumped to beat Zwick, who got a hand to the ball but couldn’t keep it out his net.
It was 3-0 in first-half stoppage-time as the visitors’ backline failed to cope once gain.
Tierney made his way into the United box and was upended by Fraser. Referee Craig Thomson pointed to the penalty spot and Commons blasted the spotkick past Zwick.
Commons was on target again on 54 minutes, this time slamming the ball into the far corner of the United net after the visitors failed to clear a corner.
The Tangerines were desperate for even a single chance and they got one thanks to sub Adam Taggart, who had just replaced Bodul.
Taggart found space inside the Celtic box to hook the ball goalwards on 57 minutes and it would have gone in had Commons not booted it off the line.
Zwick pulled off a brilliant save to keep out a drive from Stefan Johansen and Mackay-Steven went close before United brought on Simon Murray for Telfer, while Ciftci and Thomas Rogic entered the fray for the hosts.
Jozo Simunovic kept Zwick busy with a long-range strike on 77 minutes then Hoops goalie Craig Gordon and Boyata got into a muddle at a Mckay cross but it came to nothing for United.
A Ciftci header threatened to add to the Celtic tally then they did make it five in the final minute when Brown went on a mazy run before sneaking trhe ball in off the hapless Kuhl.
Celtic: Gordon, Ambrose, Simunovic, Brown, Griffiths (Ciftci 65), Armstrong (McGregor 73), Commons (Rogic 65), Mackay-Steven, Boyata, Johansen, Tierney. Subs not used: Bailly, Blackett, Bitton, Lustig.
Dundee United: Zwick, Dillon, J. Souttar, Mckay, Rankin, McGowan, Telfer (Murray 66), Durnan, Fraser (Connolly 90), Kuhl, Bodul (Taggart 54). Subs not used: Szromnik, Donaldson, H. Souttar, Robson.
Referee: Craig Thomson.