Thomas Mueller says Bayern Munich fans can not expect another miracle fight-back, like they saw against Porto, following their 3-0 semi-final drubbing at Barcelona in the Champions League.

Lionel Messi's inspired performance saw Barca score all three goals in the final 17 minutes with the midfield maestro netting twice in three minutes to stun Pep Guardiola's Bayern before putting Neymar through to score the hosts' third goal.

Messi's magical footwork at the Camp Nou for his second left Germany defender Jerome Boateng flat on the turf in a move former England international Jamie Redknapp described as "almost illegal".

"They completely fell apart, that should have never happened," fumed Bayern's honorary president Franz Beckenbauer.

"It would be a sensation now to turn this around."

The defeat means the Germans must score at least three goals in the return at Munich's Allianz Arena on Tuesday to reach the June 6 final in Berlin.

But Mueller said their fans can forget another fight-back which saw Bayern reach the semi-finals with a 6-1 quarter-final drubbing of Porto at home having lost 3-1 away.

"You can expect the return leg to go the way it did against Porto, but the 11 guys on the pitch will give their all once more until the last second," said Mueller, who argued with Guardiola after his second-half substitution.

"Now we have to stand together as a team.

"We are FC Bayern and we'll keep our heads up."

Bayern's dreams of a treble-winning season have evaporated in a little over a week after their German Cup semi-final exit on penalties to Borussia Dortmund last Tuesday and their heavy defeat in Barcelona having wrapped up their 25th Bundesliga title 10 days ago.

While it is mathematically possible for Bayern to progress, they need a footballing miracle similar to Deportivo La Coruna's 4-0 rout of AC Milan, having lost the first-leg 4-1 in Italy, in the 2004 quarter-finals.

But no side has ever come back from losing the first-leg 3-0 in the semi-final of the Champions League or European Cup -- especially against Barcelona.

"The last drop of hope is the game against Porto," inisted Bayern's optimistic goalkeeper Manuel Neuer.

"Never say never."

But Guardiola said Messi made the difference as the Argentinian ruined Pep's homecoming on his return after winning 14 trophies in four years with Barcelona from 2008-12.

"We did well for a long period," said Guardiola before the game fell dramatically away from his team on 77 minutes.

"We wanted to control the game and keep the ball away from Barcelona as much as possible -- which we did.

"But Messi simply made the difference and it's a pity we conceded the third goal.

"The return leg will now be complicated, but we will fight hard."

Injuries have cost Bayern dearly in recent weeks with wingers Arjen Robben, who has scored 19 goals this season before tearing stomach muscles, then his calf on his return, and Franck Ribery both sidelined.

Striker Robert Lewandowski played with a mask in Barcelona after fracturing his cheekbone and nose in the defeat to Dortmund.

"You can't complain about the way the team has performed up until now, they fight and give everything," said Bayern's director of sport Matthias Sammer.

"Against Barcelona, we were pushed to the limits because of the whole situation.

"We stood up well for 77 minutes against a team that is at the top of its game and are probably the best in Europe.

"We lost a bit of our order at the end and tried too hard.

"We'll be at home in the return leg and our fans need to get behind us.

"We need to shake off this defeat and digest the result."