Daizen Maeda is away down the left for Celtic, but a second ball is thrown on to the pitch from the home end and it halts a promising attack.

Well the referee hasn't gone to the screen, and play goes on. Porto aren't happy.

Real debate in the office over that challenge. Emmanuel Fernandez does get the ball first, but he also clatters Pepe - albeit low down on his ankle.

For those who have seen it... Fair challenge? Thumbs up. Penalty? Thumbs down.

Utrecht swing a corner to the back post and there's a brief moment of panic before it's headed behind for another corner.

The visitors still haven't had a shot.

Alasdair Lamont
BBC Sport Scotland in Porto

A tough few minutes for Rangers having looked composed until the equaliser went in.

Emmanuel Fernandez again showing his worth with an incredible turn of pace and fabulously-timed challenge to deny Porto an almost-certain second.

The home fans were adamant it should have been a penalty but the officials weren't swayed by their hostility.

Image source, SNS

Porto go in search of an immediate second. Pepe glides by James Tavernier and gets into the box...

He goes to pull the trigger and Emmanuel Fernandez slides in hard, taking the ball and the man, absolutely crunching Pepe.

There's a penalty check now on that challenge.

Daizen Maeda puts his head in among the boots, but he nods Benjamin Nygren's cross wide.

A tough chance for the Japan forward.

Utrecht are bottom of the Europa League table with one point.

Celtic have been excellent in the opening stages, but the Dutch outfit have been very poor.

Tom English
BBC Scotland chief sports writer

Celtic running amok. Utrecht are a jittery shambles with one of their wobblers-in-chief, Vasilis Barkas, standing out. Funny, that.

Now that the knockouts look a racing certainty - they'll get a minimum of £15m this season - it might be time for the board to start pressing some buttons on transfers.

Tomorrow, surely, some kind of cavalry starts appearing over the horizon. Surely!

Image source, SNS

It's settled down a bit now in Portugal. Porto seem to be far more dangerous on the counter, and they've cut Rangers to ribbons on two or three occasions.

However, when the visitors get bodies back, they look solid and Porto can't pass through them.

James McFadden
Former Scotland forward on BBC Sportsound

It won't be a case of settling for three.

Celtic will want to enjoy themselves now.

Pat Bonner
Former Celtic goalkeeper on BBC Sportsound

What a penalty.

No goalkeeper is going to save that.

That's incredibly harsh, but Celtic will take it.

Auston Trusty's header hits the hand of Dani de Wit at such close proximity.

After watching about 1,000 replays, the referee comes back on to the pitch and points to the spot.

VAR are checking for a potential penalty for Celtic and the referee is off to the monitor...

James McFadden
Former Scotland forward on BBC Sportsound

If Celtic can go and get a third goal in the next five minutes, Utrecht will be gone.

They haven't shown anything this Europa League campaign to show they will get back into this.

Benjamin Nygren is really expressing himself tonight.

His free-kick from 30 yards out is creeping into the bottom corner before Vasilas Barkas turns it round the post.

Alasdair Lamont
BBC Sport Scotland in Porto

Incredible start to the game for Rangers, who have looked assured, carrying the confidence of a team that has won their last eight games.

Findlay Curtis justifying his inclusion with a terrific cross and Djeidi Gassama heads in his eighth goal of the season, six of which have come in Europe.

James McFadden
Former Scotland forward on BBC Sportsound

This is an outstanding start for Celtic.

Barkas didn't have a great time here and he's certainly not having a great time tonight.