Bayern Munich's coach Josep Guardiola celebrates their fifth goal during their Champions League quarterfinal second leg match against Porto at the Allianz Arena in Munich, April 21, 2015. [Photo/Agencies]

"This is about life or death and I know how very important it was," Guardiola, who was under mounting pressure after their first leg defeat and the sudden departure of the club's long-time doctor told ZDF Television.

"I know what is expected of me in this team. It is about winning just like at Barcelona. We played a different game. We knew Porto better after the first game. Now we have to fight otherwise we will not achieve what we set out to do."

Two more goals before the break from Lewandowski and Thomas Mueller, who became Germany's record scorer in the competition with 27, and a late Xabi Alonso free-kick finished off Porto, who had Ivan Marcano sent off in the 87th for a second booking.

Despite missing Arjen Robben, Franck Ribery and David Alaba among others, Bayern took the initiative from the start.

The hosts, who have won all five home games in this season's competition, made their intentions clear early on when their Poland striker Lewandowski hit the post in the 10th minute.