Martin O'Neill faced with huge Celtic decision for Rangers clash and makes Camilo Duran confession

Wolves loanee Johnstone was selected ahead of regular keeper Viljami Sinisalo for the Premiership match in Perth and made a fine save from Joel Cotterill in the first half when the scores were level.

The England internationalist was steady thereafter and was praised by O'Neill, who will now have to decide on who plays in the white-hot atmosphere of Ibrox in the Premier Sports Cup quarter-final.

"Yes, he's done very, very well indeed," said O'Neill on Johnstone. "The save was fantastic. Really, really brilliant reaction save. He's been a fine goalkeeper. It's just a matter of getting up to speed with things.

"I think he took a bit of cramp later. A goalkeeper taking cramp, whatever next. But anyway, I think Peter Shilton took cramp way back in 1979 as well too, so I shouldn't complain."

O'Neill revealed that he held discussions with Sinisalo prior to facing Saints about why Johnstone was playing. "Yes, I spoke to him, and he's taken it," said the Northern Irishman. "We'll see what happens on Sunday. But we've got loads and loads of games, and it is really nice to know that I have actually two really decent goalkeepers."

Johnstone was one of five changes to the Celtic team in Perth, with centre-half Cameron Carter-Vickers left out completely for Dane Murray after starting every match so far this season. O'Neill hopes to have the American back for the Old Firm clash.

"I'm hoping that he would be available, yes, for us," said O'Neill. "He hasn't hardly missed a minute of pre-season, and also the games. He's been out for a year, and he was just feeling really sore on Saturday evening.

"I've got much time for big Dane Murray. I've got a lot of time for him. I think he's got a proper career. His injuries have curtailed him for a while, but he's just coming through. I think he's got a really decent future, and things to pick up on. But yes, in terms of Carter-Vickers, he should be okay for Sunday."

In-form forward Camilo Duran was used from the bench, with O'Neill keeping the Colombian fresh for Rangers. "He's just been class," said O'Neill. "He looked tired in the game against St Mirren. But I'm not surprised for the amount of things that he does for us, both with the ball, which is terrific, and also the work that he does off it.

"He's second only to Daizen Maeda in terms of closing players down. So I wanted to try and see if we could do without him, and the answer is probably not!"

Celtic merited their victory over St Johnstone but took a while to hit their stride, with Mika Baur's 52nd-minute goal the difference between the two teams.

On the performance as a whole, O'Neill added: "I don't know, I really don't know. I thought we started off with a lot of possession. I thought we started to create a few things. When we were doing that, it looked as if there was nobody in the penalty box for us.

"Then Sam makes a great save, which is a big, big moment in the game for us. Because it could have been Saturday night [against St Mirren] all over again. We got a bit more tempo into the game in the second half, got the goal and saw it through.

"We could have scored a number of goals, but we made that look very, very difficult indeed."