IT'S amazing how calm a player can be when he doesn't realise exactly what's going on.

Nearly 60,000 pairs of eyes were fixed on Kris Commons in the moment when Celtic's Champions League group came to the boil, yet he never felt the heat. Celtic had a penalty to beat Spartak Moscow, with just eight minutes of the match remaining, and Commons was as cool as you like. It even crossed his mind to "do a Panenka" and dink the ball over the Russians' enormous goalkeeper. Commons is an impressively nerveless character at the best of times but how could he be quite so composed when a place in the last 16 hinged on his penalty? Simple: he didn't realise it did.

Something odd happened in the second half of the Spartak match. Plenty has been said about the influence a packed Parkhead has on the Celtic team, and the supporters' ability to lift and inspire players is beyond question. But on Wednesday the crowd also did something entirely different: it unwittingly misled the team. A cheer swept around the stands in the opening minutes of the second half, suggesting Barcelona had scored against Benfica. In fact it was a phantom goal – the game at Camp Nou finished goalless – but some Celtic players did not realise that until game was over.

The rumour could have had horrible consequences. It was dangerous for Celtic to be under the impression that a draw with Spartak was good enough to take them through because Benfica were losing. In fact, if Commons hadn't scored, they would have finished third in the group and dropped out of the tournament.

Commons could afford to reflect on it all with a smile across his face at Lennoxtown yesterday. "When I got the penalty, I thought Barcelona were winning. No-one came to me and said 'listen mate, you need this to go in'. Our fans had been standing up and cheering. I thought 'happy days, Benfica are losing and they need a goal, Barcelona will probably get another two or three like they usually do so we just need to hang on'."

The mood and messages were mixed. "There was a lot of anxiousness around the stadium, as if it wasn't all going our own way. I saw Lassad [Nouioui] coming on and I thought 'that's a strange sort of substitution if we don't need to win' and the gaffer came on to the touchline geeing us up. I thought to myself 'why's he doing that'. I was looking around and the crowd weren't themselves; they weren't singing or bouncing. But I had no idea that Barcelona were drawing. We got the impression they were winning. Earlier all the crowd were cheering and we were looking around at each other thinking 'they must have scored'. It was only when I was in the treatment room [he went off with a thigh injury] that someone said 'we're through, Barcelona drew nil-nil'. I thought they were winning."

Commons' false sense of complacency served one purpose: it made his penalty – after Georgios Samaras folded under a humdrum Marek Suchy challenge – seem less daunting than it actually was. "I put the ball down and I wasn't thinking 'this is to take us into the last 16'. It helped that, at the time, I didn't think a win was essential. I suppose it's the sort of stuff you dream about as a boy but it's one thing to do it on a park or in training and another to do it in a game when there is something at stake. But I just thought it was a normal penalty. I actually took a step on the way to the run up and thought about watching to see if he dived early and dinking it, but on my second step I just smashed it."

Commons' kick hit the crossbar. Maybe last season, when so much went wrong for him, it would have bounced out. Not now. It smashed down over the line and allowed him the headlines he deserved from an excellent individual performance in a campaign which has contained many of them. Commons has recovered fitness and form, recovering the levels of creative menace and goalscoring he showed in his outstanding first few months at Celtic.

He has looked so accomplished that it was surprising to hear him express self-doubt yesterday. "For me, playing in the Champions League has opened up my eyes that I am capable of playing at this level and mixing it with these players. My family is pretty poor and I come from a relatively rough area. I was playing for average little teams when I was a young kid. It's weird for me, I laugh and joke with Kelvin [Wilson] about it. At Nottingham Forest we were in League One playing at Cheltenham and Leyton Orient trying to get promoted back to a level that was respectable. You go to these places and play on cabbage patches in front of 3000 fans. That's only five or six years ago, and now we're part of one of the 16 elite clubs in Europe.

"When my brother Spencer sees me on television he can't believe he's seeing me in the Champions League. And I'm scoring to get Celtic into the last 16. It just seems surreal because I feel like I don't really belong there. My brother is a sparky. He played football in the same side as Kelvin but, when he was 16, he broke his ankle and dislocated it at the same time, so that was him finished. I sort of owe him a lot.

"People used to say to me 'your kid's better than you' so when I play I feel I am doing it for both of us. He went from being a young kid breaking into the first team at Notts County, to fixing light fittings. But he comes and fixes my lights all the time. I have to keep him sweet."

He does a fine job of that. With that unflappable penalty he kept plenty of others sweet too.