Chelsea are flooding the final third with bodies now and Atletico are grateful for a soft free-kick when Demba Ba's strong challenge takes out Thibaut Courtois. A promising attack is snuffed out.

Jonny Pickles:, external Diego Costa celebrating against his potential future employers. Disgusting behaviour.

It sounds daft, but it all started to go wrong for Chelsea the minute they scored. It seemed to galvanise Atletico and the Blues' defence crumbled.

Adrian Lopez, who has just been booked, is taken off by the excitable Atletico bench and replaced by Raul Garcia. Jose makes a change too - sending on Demba Ba in place of Fernando Torres.

Paul: OK, answers on a post card. Who will Jose blame this time other than his poor tactical choices? Penalty right and Atletico deserve the lead.

Willian's set-piece delivery has caused Atletico problems all night and the gifted Brazilian almost drags Chelsea back into the tie when his delightful ball is powered against the post by the head of David Luiz.

Robbie Savage
BBC Radio 5 live

"What a penalty from Diego Costa. After the long delay he showed nerves of steel there to blast it into the roof of the net."

Image source, Getty Images

He took his time, but Diego Costa keeps his nerve to send Mark Schwarzer the wrong way and seemingly send Chelsea tumbling towards a Champions League exit.

Strange scenes as Diego Costa is shown a yellow card for taking too much time over his spot-kick. He's concerned about a small hole on the penalty spot. It all adds to the drama...

Image source, Reuters

Massive! Diego Costa nips the ball around Samuel Eto'o before being brought down by the clumsy striker. The referee instantly points to the spot. I think he's right too.

Andrew in Belfast: Chelsea find themselves in a very unfamiliar position in a big game. They now have to attack and take the game to their opponents. I wonder do they still remember how to do that?

Robbie Savage
BBC Radio 5 live

"Azpilicueta has got the wrong side of him and it has to be a penalty. The referee has to give it. What a let-off for Chelsea."

Oooh, a let-off for Chelsea when Arda Turan goes tumbling in the area under Cesar Azpilicueta's clumsy challenge. Atletico are livid, but we must move on deems the referee.

Image source, Getty Images

It's time for a bit more adventure from Chelsea as Samuel Eto'o replaces Ashley Cole.

What a fine save from Chelsea's, I mean Atletico's, Thibaut Courtois. The on-loan stopper gets down well to beat away John Terry's powerful, goal-bound header from Willian's free-kick.

To their credit, Atletico are going for that killer second and Tiago's daisy-cutter briefly tests Mark Schwarzer in the Chelsea goal.

Ben Channon:, external I appreciate respecting your old club, but not celebrating is disrespectful to your current club's fans.

Jamie Matthews:, external I don't mind players not celebrating out of respect, but I didn't like Shelvey apologising against Liverpool. No need for that.

You get the feeling that this second half will slowly build to a crescendo - rather like in the last round against Paris St-Germain. Can Chelsea end on a winning note though?

Somebody's taken the handbrake off the bus and it's rolled off the pitch. Chelsea's defence is, once again, all over the shop when Koke drills an innocuous ball into the box and it arrives at the far post where Arda Turan brings a point-blank save from Mark Schwarzer.

As both sides walked down the tunnel for the second half, Jose Mourinho was bending the ear of the referee. I wonder what he might have been saying? Anyway, we're back under way in a second half in which Chelsea MUST score if they are to go through. This tie can't go to extra time now and, as it stands, Atletico are going through on the away goals rule.