Celtic manager Ronny Deila says his side can't be expected to win all their games comfortably after the Scottish champions claimed a hard-fought 2-1 win over St Johnstone at McDiarmid Park.

The Hoops made a perfect start when Leigh Griffiths fired home the opener after just 35 seconds on Saturday and only a series of good saves from St Johnstone 'keeper Alan Mannus kept the Scotland international and his teammates from adding to the scoreline.

Stefan Johansen added a second early in the second half to seemingly put Celtic on course for another routine victory.

However, Michael O'Halloran's 72nd minute strike, the first goal Celtic had conceded since December 21, gave St Johnstone a glimmer of hope.

It extends Celtic's winning start to 2015 to eight matches in all competitions ahead of their crucial Europa League last 32 first leg clash at home to Inter Milan on Thursday.

"It's all about winning and we did that today. You can't go through every game and just be comfortable," Celtic manager Deila said.

"We always go out to play at 100 percent and we should have scored more goals on the chances we created.

"I think the players worked hard for 90 minutes and at 2-0 it seemed quite comfortable. I think we produced a lot of chances and were direct.

"Then we conceded a goal and everything turned around and they put pressure on us. They were very aggressive and played very direct and were good in set plays as well, so we needed to defend well in the end.

"We played three days ago and in the end the players started to get a little bit tired.

"St Johnstone are hard to play against and I'm very happy with the three points."

Only a superb double save from Celtic 'keeper Craig Gordon late in the game allowed his side to extend their lead at the top of the table to six points.

And Norwegian manager Deila was full of praise for the Scottish shot stopper.

"We had an unbelievable save from Craig Gordon in the end. It shows his class when you can do that when you've almost not had a save to make before it," the Celtic boss said.

"You can see every day in training how good Craig is. He is such a good goalkeeper and helped us win this game."

The goal ended a run of 816 minutes without conceding a goal for Gordon and the keeper was understandably frustrated at the run coming to a halt.

"I was annoyed we lost the first goal and didn't want to lose any more," the Celtic stopper said.

"We came close to dropping a couple of points that didn't look likely for large parts of the game.

"A lot of people have said that I've not been too busy over the last couple of games and I was delighted to make up for that and I was glad to play my part in getting the three points."

Elsewhere on Saturday, Inverness moved level on points with second-placed Aberdeen, who face Hamilton on Sunday, with a 2-1 win over struggling St Mirren.

Dundee United lost ground on the top three as Kilmarnock twice came from behind to secure a 3-2 win at Rugby Park, rivals Dundee moved into the top six with a last minute winner against Partick Thistle and tailenders Ross County secured a vital 3-2 win over Motherwell.