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Inverness defender Josh Meekings does a fair impression of someone who has just made a headed clearance in front of goal. But we know different...

Michael Monaghan: "#bbcscotfootball @BBCSportScot Does anyone know what the official next to the goal is for? Obviously not to spot fouls/offence in the box...!"

MBEHAN: "Clearest penalty you will see all season even with extra officials they fail to spot the most blatant hand ball & red card #bbcscotfootball"

Dougie Kinnear: "What a surprise! BBC and SKY want to talk about bad decisions when it affects celtic! No one gives a damn unless it's them! #bbcscotfootball"

TV replays may excuse the extra official behind the goal, even though he was only a few yards away from that illegal block from Josh Meekings. His view may have been obscured but referee Steven McLean has a clear line of sight. Tut, tut.

BBC Scotland's Tom English at Hampden

"It's a real whopper. Mistakes like that should not be made when everyone in the stadium can see it's a penalty in real time."

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BIG talking point right on half-time as Celtic are denied a clear penalty. It would have been a red card too. Ronny Deila's side lead 1-0 thanks to a wonderful free-kick from Virgil van Dijk.

Ryan Esson is busy again as he leaves his line to make a good block from Stefan Johansen. The ball spins towards Leigh Griffiths at the back post and the striker nods it on target only for Josh Meekings to stick out an arm to stop it in front of an empty net. There's an extra official behind the goal near the six yard box and he doesn't see it - neither does the referee. Controversial...

Nice footwork from Kris Commons creates room for a skidding shot from 20 yards and Ryan Esson makes an excellent full-length save.

Greg Tansey curls a corner to the back post area where Gary Warren is first to it but the Inverness defender can only head wide.

As half-time approaches, there are signs that Inverness are finding their feet again, with Ryan Christie looking comfortable on the ball in midfield.

Inverness boss John Hughes is shaking his head as a free-kick 30 yards out is played short then looped into the box by Danny Williams, making it an easy catch for Celtic goalkeeper Craig Gordon.

For the second time today, Celtic right-back Adam Matthews is late with a challenge - this time on Danny Williams - but the referee just waves play on.

Kris Commons drifts in behind the Inverness defence to try and gather a long, diagonal pass from Virgil van Dijk but can't bring the ball under control. The Celtic midfielder is complaining that his jersey was being tugged by Graeme Shinnie.

Darren Goldsby on Twitter: "Remember super cali are terrific Celtic are atrocious? Don't think it'll happen again #bbcscotfootball"

Inverness are sticking with a 4-4-2 formation but they are being swamped in the midfield area, where Celtic have an extra man.

A quick one-two from Celtic as they look for a knock-out punch. First, Scott Brown drills in a low shot with Ryan Esson right behind it, then the keeper needs to make a much more testing stop to keep out Stefan Johansen's venomous effort.

Inverness striker Edward Ofere has his head in his hands as he scuffs a shot over the crossbar from close range but the whistle had sounded for a foul at the corner kick.

Scott Brown is cautioned for a late hack at Danny Williams as the Celtic skipper breaks up a counter-attack from Inverness.

Inverness are wobbling now as Leigh Griffiths gets in behind and his cutback is hacked clear. Nir Bitton is the next Celtic player to make progress in the opposition penalty box and Gary Warren needs to make a good covering tackle.

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That's a beauty! Virgil van Dijk steps up to the set-piece and clips a lovely curling effort beyond the defensive wall and the ball flies in via the inside of the post. No chance for the diving Ryan Esson.

Gary Warren is cautioned for grappling with James Forrest and Celtic have a free-kick on the edge of the penalty box.