“First, Chelsea, then us,” said Real Madrid’s former Liverpool midfield star. “No, they are not unbeatable.”

HUMAN AFTER ALL ... Lionel Messi

IT was short, sweet and to the point — and it came from Xabi Alonso.

“First, Chelsea, then us,” said Real Madrid’s former Liverpool midfield star. “No, they are not unbeatable.”

Well, we all know who THEY are. Or we thought we did.

We thought they were the team who always had that extra bit of something with which to wriggle out of a hole. Just as they did most famously in the last minute at Stamford Bridge in 2009.

But inside four days Barcelona’s aura of invincibility has gone.

Which leaves us with two questions as we head into tonight’s breathtaking Champions League semi-final second-leg clash at the Nou Camp.

Are Barca so psychologically damaged that Chelsea, the team most observers thought had little or no chance before their 1-0 victory in West London last Wednesday, really can end the Catalans’ hopes of becoming the first team to retain the Champions League trophy?

Or, alternatively, will Chelsea’s recent luck finally run out as Barcelona finally recapture the form that made them a team apart?

The Blues have lost once in 14 games since Roberto Di Matteo took over. But even their staunchest supporters will admit they have needed a sizeable slice of good fortune.

There was the frantic last 10 minutes against Benfica at the Bridge, the two offside goals against Wigan and, though they would eventually pulverise Spurs in the FA Cup semi-final, they did initially require the helping hand of the goal that never was to make it 2-0.

Then came the missed Barca chances in the first leg and two other efforts that came back off the woodwork.

Finally, Arsenal were denied on Saturday by the crossbar and, most surprisingly of all, a miss at the far post by Robin van Persie.

Surely, this cannot continue. Surely, in front of their own fans, Barcelona will finally get the break denied them and the others over the last month.

Surely, Lionel Messi will finally score against Chelsea.

We will find out soon enough.

Barca’s self-belief took another huge dent as Real Madrid won at the Nou Camp on Saturday night to inflict Barca’s first home defeat in 55 games.

And Pep Guardiola’s tetchy reaction last night to criticsim of his team selection for El Clasico showed he is a manager on the edge.

By pushing Messi deep and cutting off his supply, Jose Mourinho’s side suddenly made the world’s greatest player look more like the under-performing Messi of Argentina.

Suddenly the 24-year-old scorer of 63 goals this season looked jaded. Suddenly the tricks weren’t working.

When Messi cannot provide the answers, Barca do look fragile.

But how much do the Chelsea vets have left in the tank?

You somehow doubt whether Frank Lampard and Didier Drogba, if fit, will last more than 70 minutes. And how much longer can John Terry and Gary Cahill get battered bodies in the way of shots?

The bookies have Barca as comfortable favourites and it is hard to argue. But, increasingly, it looks like a game that will be won as much in the mind as anywhere else.