Two goals, two banners, one injury and a game still firmly in the balance.

Kevin Kilbane
Former Republic of Ireland winger on 5 live

Sanchez has a couple of minutes to get through to half time and then he can be assessed properly in the changing room. 

He doesn't look that great though - he isn't moving well. 

Three minutes of injury time. Arsenal are on the attack, looking to strike a big blow before the break. Sanchez is in the thick of it, showing few effects from the earlier foul. He loses control, though, and a chance evaporates.

Sanchez has been knacked by West Brom a few times this half as part of a targeting campaign. The latest one sees James McClean slide right through the Gunners forward as he looked to break. The ref waits for the attack to break down before going back to book McClean. Sanchez receives some treatment and limps away after getting to his feet but is going to try and continue.

Cech is a big loss for Arsenal. Sanchez would be a catastrophe. 

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Optimistic. Granit Xhaka has a pop from way out but it lacks power and precision and the ball floats tamely wide to ironic home cheers.

Kevin Kilbane
Former Republic of Ireland winger on 5 live

We know what West Brom are like with set pieces - 13 goals from corners this season. David Ospina now has got to be aware of that. 

This brings a certain amount of uncertainty.

Cech clearly has a muscle strain but he is walking all the way off the pitch. He has a member of the medical staff with him but he's not getting a shoulder to lean on.

On comes David Ospina, whose most recent action involved picking the ball out of his net 10 times over two games against Bayern Munich.

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Oh no. This doesn't look good for Arsenal. Petr Cech goes down and it quickly becomes clear he will not be able to continue. It came from playing a short pass to his own defender.

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Kevin Kilbane
Former Republic of Ireland winger on 5 live

Great passage of play there from Arsenal. Good strong arm from Foster to palm it away. 

And then another brilliant save from Petr Cech at the other end... It's been a great game so far! 

Now West Brom go close. Really close. Darren Fletcher has just Petr Cech to beat but the keeper comes out on top, tipping aside his powerful, goalbound drive from inside the box. The corner causes more panic but the Gunners survive.

How have Arsenal not scored? Aaron Ramsey's angled shot from inside the box is tipped away by Ben Foster but to the edge of the six yard box where Theo Walcott surely only needs a neat touch to find the net but can't beat Nyom, who blocks.

Salomon Rondon's first real sight of goal is spurned as he pulls an effort from inside the box wide of the far post. He had the attentions of a couple of defenders, who did their job well.

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James McClean is finding a lot of space down the left. He charges away again but this time over-hits his cross to the far side allowing Arsenal to rally.

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Kevin Kilbane
Former Republic of Ireland winger on 5 live

West Brom look comfortable from a defensive point of view but it's when they get the ball, they are finding it hard to get into the game. 

Pulis must be worried that they conceded so quickly after getting themselves in front - the game seems to be following that pattern now. 

More panic at the back. The ball is swung in to the danger zone, with home players flinging themselves in to get a touch but the final and decisive touch comes from an Arsenal boot to clear. A foul on Alexis Sanchez gives the away side some respite.

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This game is being played out to the constant buzzing of planes overhead as the pro and anti Wenger aircraft compete for supremacy. Meanwhile, West Brom have another corner. Time for Arsenal to switch on...

Alexis Sanchez isn't happy. He thinks Jake Livermore has fouled him on the edge of the box. He has a point as well. The Baggies midfielder had two kicks at him to send him tumbling to the turf. Ref didn't think so, though.

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Tony 'Bomber' Brown
Former West Brom striker on BBC WM 95.6

What’s happened for the goal is the ball has gone to the far post and Craig Dawson has gone in. There’s a man covering but Nacer Chadli has let him go, he hasn’t spotted the danger. Tony Pulis will be furious.

Arsenal looking dangerous. Aaron Ramsey breaks down the left and chips a cross to the back post, where Nyom is fouled as he makes a clearing header.

Kevin Kilbane
Former Republic of Ireland winger on 5 live

Once Alexis Sanchez got into that position, he had so much space! 

Just watching Arsenal, they were moving so slow to begin with but then when they do pick up the pace, they can bring moments of brilliance out of players like Sanchez. 

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