Martin O’Neill believes he now can’t live without Camilo Duran after watching Celtic struggle to get over the line against St Johnstone.The champions chalked up their sixth straight league win this season courtesy of Mika Baur’s first goal for the club.The Celtic manager left six-goal Duran on the bench for 73 minutes and was dismayed that the side he started with failed to convert a string of half chances.And with Kasper Hogh’s goals drying up after a quick start to life in Glasgow, O’Neill now believes that the Colombian is irreplaceable.‘Duran has just been class,’ said O’Neill. ‘He looked tired in the game against St Mirren. But I’m not surprised with 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 manager Martin O’Neill was frustrated to see his much-changed side struggle in PerthDespite the welcome victory, O’Neill was clearly underwhelmed with his side’s poor conversion rate in front of goal.‘I thought we started off with a lot of possession,’ he added. ‘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.‘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.’O’Neill made five changes to the side, with Sam Johnstone selected ahead of Viljami Sinisalo in goal. The Englishman made an excellent save to deny Joel Cotterill with the game still level.‘He makes a great save, which is a big, big moment in the game for us. Because it could have been Saturday night all over again.‘The save was fantastic — a really, really brilliant reaction save. He’s been a fine goalkeeper. It’s just a matter of getting up to speed with things. Mika Baur was the Celtic hero after claiming his first goal since his summer transfer‘I think he took a bit of cramp then. A goalkeeper taking cramp, whatever next…’Asked if he’d spoken to Viljami Sinisalo about leaving him out, O’Neill said: ‘Yes, he’s done very, very well indeed. But you need to find out. While I do not want to use games like this, I have to find out about a number of players.‘For instance, Oliver Sorensen started the game tonight. Our main man (Duran) only came on in the last 10 or 15 minutes. So, it does, it gives you food for thought.’Cameron Carter-Vickers wasn’t in the match day squad, but O’Neill is optimistic that he’ll be available to face Rangers in the Premier Sports Cup at Ibrox on Sunday.‘I’m hoping that he would be available, yes,’ he explained. ‘He’s 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. Camilo Duran was restricted to the bench until being called upon with 17 minutes to go’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 OK for Sunday.’Kieran Tierney is also ready to play at Ibrox having come in as a late substitute.‘It’s nice to see him,’ he added. ‘We were trying to get him on the field before the end of the game.‘Even if he’d not got on, he’d have been alright for Sunday.’