Scott McDonald believes the Old Firm are taking it in turns to be "in turmoil."

McDonald was instrumental in taking Celtic two points clear of Rangers in the Clydesdale Bank Premier League with a 3-1 home win over St Mirren.

The victory came hours after Rangers, who crashed out of Europe in midweek by losing at home to Stuttgart in the Champions League, lost 1-0 at Aberdeen.

St Mirren defender Chris Innes deflected a McDonald drive past Buddies goalkeeper Paul Gallacher to give the home side the lead in the 38th minute and Georgios Samaras made it 2-0 three minutes from the break.

Substitute Michael Higdon gave St Mirren a lifeline before the interval but McDonald sealed the points with a close-range strike just after the hour to give Celtic only their third win in 11 games.

He said: "Consistency is the key in this league. There is none of that going on.

"Ourselves and Rangers keeping giving each other a lifeline. It's us one week and them the next. One club is in turmoil one week and then it is the other.

"If we had had a good run in the league then by now we would be away from the rest."

McDonald was involved in a moment of farce with seconds remaining after Innes had conceded a penalty with a blatant handball.

Referee Steve Conroy, thinking he had booked the former Gretna player earlier, sent him off, only to bring him back on after realising he had made a mistake.

McDonald had his penalty saved by Gallacher, who also blocked the rebound.

The Australian, though, appeared to believe he had been denied a hat-trick.

"Someone told me that the first goal was an own goal and I gave him a strange look," he said. "It took a little nick off him but it was going in.

"The missed penalty will ruin my night even though it was a good performance. But the second save was very good. It is nice to get two goals, especially at Celtic Park."

Not for the first time this season, thousands of Celtic fans stayed away, a fact not missed by McDonald.

"It is noticeable," he said. "There are lots of empty seats but it is up to us to put in the performances to bring them back and I 'm sure they will come back if we do that."

Celtic manager Tony Mowbray was pleased with the points but reiterated his desire for good performances.

"The three points were the most satisfying thing," he said. "We try to play with style and we work on things but ultimately it's about taking the points and it's been a good weekend for us.

"But I will always be a performance-related coach because good performances give you consistency of results.

"You can scramble a victory every now and then but you ain't going to do it every week.

"If your performances are not of a good enough standard you are not going to scramble 1-0 or 2-1 wins every week.

"You will draw or lose games so we strive for high performances."

Mowbray refused to discuss reports that he had been in France on Friday night to watch Tours striker Olivier Giroud in a Ligue 2 clash with Angers.

He said: "There have been a lot of other trips over the last few weeks that people have not talked about but it's a part of a process that we are going through to try and identify footballers."

St Mirren boss Gus MacPherson had no qualms about referee Conroy's mistake, claiming an earlier infringement in the game had been more costly.

"Steve is a good referee and he will be highly embarrassed about that," he said. "It was an unusual mistake but I'm not upset.

"I'm more upset with the free-kick that we should have had before Celtic's first goal.

"It was quite clearly a foul on Stephen McGinn by Andreas Hinkel at the edge of the Celtic box.

"We can't shout too loudly about it because we got possession back and gave it away again.

"So I'm not going to complain about clerical errors."

MacPherson revealed that Andy Dorman went off with a hamstring injury and will await further diagnosis at the beginning of the week.