Dundee United laboured in the May Day sunshine at Celtic Park on Sunday, with the title-hungry Hoops forcing them to put in a hard shift.
United brought back stalwart Dillon and departing midfielder Morgaro Gomis following suspension.
Dillon slotted in at right-back as boss Houston kept the central defensive partnership of skipper Kenneth and Severin intact.
In-form frontman David Goodwillie was sole striker but he was to be supported by Craig Conway and Danny Swanson whenever a break was on.
The Hoops were along familiar lines but there was no place for Greek forward Georgios Samaras, fresh from his penalty miss at Ibrox a week earlier.
Celtic’s James Forrest had the first attempt on goal on two minutes and it was a vicious shot from inside the box that United keeper Dusan Pernis did well to punch away.
Severin then did well to block when home midfielder Kayal raced down the right then shot, while the pressure continued to pile on the visitors as Daniel Majstorovic headed over a Kris Commons corner from close range.
The Tangerines had a go themselves on 10 minutes and they were pretty close to the opener. Dixon swung over a dangerous cross from the left and first Swanson then Prince Buaben tried to connect with headers but the ball flew over the heads of both.
Commons was seeing plenty of the ball and he was nearly the architect of a goal when he kept his feet well inside the area then stabbed the ball to Anthony Stokes, who flicked it on to the far post and away again.
United were getting pinned back by Celtic’s wide play but, when the Tannadice men hit on the break through Conway on the quarter-hour, his ball to the far post was just too hard and early for the inrushing Swanson to catch.
With 22 minutes on the clock there was a huge roar from the home fans as Scott Brown went down inside the box following a challenge by Scott Robertson, but the United man appeared to get the ball.BlunderBut the Hoops were not to be denied just a minute later when a blunder by Kenneth opened the door for them.
The defender stumbled when in the right-back position but seemed to recover.
However, his attempted passback to Pernis fell well short. Stokes took control and crossed low for Hooper, who tapped in at the back post to make it 1-0.
Celtic were on song now and Stokes had the home fans on their feet again when he tried a long-ranger that zipped past the diving Pernis’ left-hand post.
As United tried to regain their composure, a long punt upfield by Pernis on 42 minutes made its way to Goodwillie, who won the physical battle with Kayal inside the Celtic box, then cut in before firing in a shot that was blocked.
Kayal was then caught out again, this time by Conway, but somehow he escaped a booking for his cynical challenge on the United man.
The Tangerines started the second period well and passed up a tremendous opportunity to level just four minutes in.
As they swept up the left, Buaben suddenly found space as he raced into the box. He laid the ball on a plate for Gomis but his midfield mate made a hash of his shot and the ball spun away to safety.
Celtic then came close on 52 minutes but Kenneth this time was the hero, clearing a netbound shot from Stokes, then chesting the ball away again when Brown pounced on the rebound.
Two minutes later it was 2-0, though, and it was a wonder strike from Kayal that raised the roofs off the Celtic Park stands, with the Israeli ace letting fly from 30 yards and leaving Pernis with no chance.
The Tangerines had to go for it now and Houston brought on attacking options Jon Daly and Johnny Russell, with Buaben and Swanson making way.
Russell nearly made a remarkable and instant impact, dribbling through the Celtic defence before cracking the ball off the base of Fraser Forster’s post with the Celtic keeper rooted to the spot.
Russell had livened up the visitors and he beat the offside trap on 62 minutes when picked out by Gomis but the angle was too acute to trouble Forster.
As the visitors tried to find a way back into the match, Daly had a cross plucked off his head by Forster, then Gomis fired a 25-yard shot just over the bar.
Kenneth sent a blistering cross over from the right that Goodwillie tried to connect with as Forster came out of his goal, but the ball just did not fall for the Tangerines.
Celtic were showing some jitters despite having the luxury of a two-goal advantage and, when Dixon played a free-kick into the box, Forster fumbled at the first attempt before gathering just as Goodwillie was ready to shoot.DeservedUp at the other end, Pernis did well to punch away a Commons shot with seven minutes left, but the Hoops wrapped up the game with a third goal on 85 minutes and it was the lively Commons who got a deserved counter.
United were on the back foot as sub Shaun Maloney raced up the left after Charlie Mulgrew had played the ball forward.
Kenneth couldn’t cut out the cross and it was only half-cleared to Commons, who drilled home low past Pernis.
With the game one minute into stoppage time, United showed they still have bags of character by nicking a late consolation goal.
Daly found time and space up the left wing, swung the ball over to Goodwillie at the far post, then the Scotland striker squared to Russell, who drilled the ball home from six yards.
However, Celtic had the last laugh when sub Murphy, who had come on for skipper Brown on 86 minutes, ran across the defence before finding a spot past Pernis.
There was still time for Daly to get booked by referee Iain Brines for a foul on Mulgrew that was no worse than the one Kayal got away with in the first half.
That riled Houston, who said, “I was really disappointed with the refereeing.
“The reason is that I can’t understand Conway nicking the ball past Kayal and Kayal taking him out.
“It is not my style to want players to get sent off or yellow carded. But to me that was a stonewall yellow card.
“Then, with seconds to go in the game, Jon Daly does the same to Charlie Mulgrew-a second too late and it was in the Celtic half.
“I asked the referee for an explanation in the tunnel and his explanation was that on another day the Conway one would have been a booking.
“What does that mean? What is that all about?
“Surely on any day it could have been a yellow card. Are we going to decide that because it’s a sunny day you are not going to give it?
“I am now going to speak to (SFA head of refereeing development) John Fleming because I need an explanation.
“I don’t understand why he said that.”Attendance: 48,599.
Celtic Forster, Izaguirre, Majstorovic, Stokes, Brown (Murphy 86), Wilson, Mulgrew, Commons, Kayal, Forrest (Ki 65), Hooper (Maloney 75). Subs not used-Zaluska, Rogne, Samaras, McCourt.
Dundee United Pernis, Dillon, Dixon, Kenneth, Severin, Conway, S. Robertson, Swanson (Daly 57), Buaben (Russell 57), Gomis, Goodwillie. Subs not used-Banks, D. Robertson, Douglas, Watson, Armstrong.
Referee Iain Brines.
Victory moved Celtic to within one point of SPL championship rivals Rangers, with a game in hand to play against Inverness Caley Thistle on Wednesday.
United are now eight behind third-placed Hearts with three matches to go in their quest for a guaranteed Europa League place, so it looks like they may have to be content with fourth, still a creditable achievement given all their selection woes this season.
It was always going to be difficult enough for the Tangerines to contain Neil Lennon’s men but they inflicted a lot of the damage on themselves, gifting the crucial opening goal to the hosts on 23 minutes when Garry Kenneth’s blunder led to Gary Hooper making the breakthrough.
There was not a lot they could have done to stop the wonder strike from Beram Kayal, then Kris Commons made it 3-0 before United sub Johnny Russell grabbed one back.
Daryl Murphy wrapped things up for Celtic with a fourth, deep in stoppage time, that saw him run most of the United half unhindered.
“I think it was one of our worst defensive performances of the season,” said United boss Peter Houston.
“I think Celtic got their goals easily.
“I don’t want to take anything away from them but if you look at the first one we were on the attack, then the ball came out to the halfway line and Morgaro Gomis turned back the way.
“Garry Kenneth was sloppy and slack. He knows it himself and it’s not like him.
“Jumping to the fourth goal, Murphy picked the ball up on the halfway line and there were four tangerine jerseys beside him. He was still allowed to run some distance and score.
“Defensively, I thought I put our most experienced back four out today (Paul Dixon, Kenneth, Scott Severin and Sean Dillon) but it did not look that way.Punish”If you are going to give goals away like that then a good team like Celtic are going to punish you and that’s what they did today.
“We went down to 2-0 before we started to believe in ourselves. We passed the ball for fun against Kilmarnock last week but today it looked like we did not have enough belief.
“I just don’t think we were anywhere near the standard we set ourselves.”
United defender Dixon revealed Kenneth had offered his apologies for his mistake.
“We lost silly goals and in any game that is not going to help you,” said Dixon.
“At the first goal, Garry has just played it against Anthony Stokes and it has rebounded for him and the rest is history.
“He usually boots the ball in the stand.
“He was quiet in the dressing room because he knew what he had done… but he did say sorry to the boys.
“He will learn from it and won’t do it again I am sure.”
Happy Hoops boss Lennon can look forward to the midweek trip to the Highlands with relish.
“We were brilliant from start to finish,” said Lennon.
“When you make the chances we do you always want the second goal and when it came we never looked back.
“Going forward we were very, very good and defensively I was pretty happy with that too. It was a very good day.”