Why on earth is Philipp Lahm retiring? The combination of the fullback with Arjen Robben is as good as anything in football today and the two again carve open Arsenal with Robben driving a shot just over.

Robert Lewandowski gets a nudge off Gabriel as the two challenge for a lofted ball into the box and Lewandowski crumples to the floor. Again the Bayern fans want a penalty but the referee, correctly, isn't interested. Goal kick Arsenal but immediately Bayern regain possession. Full-time can't come quick enough for the Gunners.

Last throw of the dice for Arsenal as Olivier Giroud comes on for Francis Coquelin.

Image source, Reuters

Chris Murphy: A good manager who has taken Arsenal as far as they can go - tonight's scoreline proves that. Wenger leaving is progress

Mat Atahari: What just happen? I went to the toilet at 1-1, I came back and it's 4-1. Nice work Arsenal. Now I could get ready for bed.

Al Meir: Mustafi is woeful. Poor positioning and/or decision-making for the last 3 Bayern goals

Image source, Reuters

All hope is not lost for Arsenal. If they can get a second goal then it keeps things alive for the return leg. The problem is it is like a training session for Bayern Munich at the moment. 

There's shouts for a penalty as Robert Lewandowski goes down in the box after getting caught between two defenders. Nothing given.

Alexis Sanchez is the only Arsenal player trying at the moment. He chases down two Bayern Munich players, a hopeless task as Bayern do not look  concerned or in danger, but he's trying anyway.

Mesut Ozil, by comparison, has been anonymous. This was the perfect platform for him to make an impression but it has just not happened.

Bayern Munich are toying with Arsenal now, spreading play from one side of the pitch to the other.

The visitors just cannot get near the ball.

Napoli are not quite capitulating like Arsenal in Madrid but Real are dominating at the moment. Damage limitation appears to be the order of the day now for the Italians.

Image source, AFP

Pat Nevin
Ex-Chelsea winger on BBC Radio 5 live

You can feel the mess beginning to happen. It's a terrible deflection and there's nothing David Ospina can do about it. It's 4-1 and it actually could have been six by this point in the second half. This second-half start from Bayern has been extraordinary.

The loss of Laurent Koscielny was a hammer blow for Arsenal. They've just not been able to stem the tide of Bayern attacks.

Arsene Wenger makes a change as on comes Theo Walcott for the ineffective Alex Iwobi.

A pretty thankless task having to come on at this point.

Image source, Reuters

Arsenal are having to defend for their lives at the moment.

They escape first as Arjen Robben's close range shot is deflected wide before David Ospina saves Javi Martinez's header at point-blank range.

Granit Xhaka picks up a booking.

In other unexpected news, the night is dark.

Another 5-1 on the cards? This could get very, very messy for Arsenal. Bayern have just moved up a gear and the Allianz Arena is now a cauldron of noise. 

Arsene Wenger could have some interesting thoughts about Bayern's second at full-time. He appeared disappointed that the goalkick from which Bayern attacked and scored from was originally given as an Arsenal corner.

Pat Nevin
Ex-Chelsea winger on BBC Radio 5 live

It's the most sickening sucker punch for Arsenal. They tried to have a go this half but by doing that they've left themselves open at the back. It's a beautiful backheel from Robert Lewandowski.

Pat Nevin
Ex-Chelsea winger on BBC Radio 5 live

I've been impressed by a number of things in Arsenal's game. Alex Oxlade-Chamberlain and Alex Iwobi have not done a lot going forward but boy they've worked their socks off getting back.

Gabriel's first action is to hook away a cross from in front of Robert Lewandowski. Vital challenge.