With all the first-leg ties completed, we look ahead to the second set of matches to see who are the favourites to progress to the semi-finals.

Barcelona 4-0 Bayern Munich

After Bayern Munich's demolition of Sporting Lisbon in the previous round, most people were predicting that the Germans would give Barcelona a run for their money. Unfortunately it wasn't to be. Pep Guardiola's side were in a destructive mood as they knocked in four first-half goals to effectively end the tie after 45 minutes. Bayern will try to rescue some of their damaged pride in the second leg, but Barca can comfortably look forward to the semi-finals.

Second-leg prediction: Bayern Munich 2-2 Barcelona (2-6 on aggregate)

Liverpool 1-3 Chelsea

Chelsea's emphatic win at Anfield illustrates two points; Liverpool are still far from being the finished article and Guus Hiddink has spectacularly turned Chelsea's season around. By employing Michael Essien as the defensive midfielder, Hiddink managed to shackle the normally influential Steven Gerrard and without him pulling the strings Liverpool looked a different side. Rafa Benitez won't have to go too far back in history for an example of a Liverpool comeback, but at Stamford Bridge it is hard to see them overturning Chelsea's lead.

Second-leg prediction: Chelsea 2-1 Liverpool (5-2 on aggregate)

Manchester United 2-2 Porto

It may not have turned into a full blown crisis but Manchester United are definitely beginning to wobble. According to Sir Alex Ferguson, things started to go wrong at the end of February when their incredible run of clean sheets came to an end against Blackburn. Since then they have suffered defeats to Liverpool and Fulham and against Porto looked thoroughly unimpressive. The midfield three of Darren Fletcher, Michael Carrick, and Paul Scholes left the defence horribly exposed; allowing Porto's attacking players to cause havoc. United will almost certainly have to beat Porto in Portugal, something no English side has managed to do yet, but with so much talent at Ferguson's disposal you wouldn't bet against them.

Second-leg prediction: Porto 2-3 Manchester United (4-5 on aggregate)

Villarreal 1-1 Arsenal

Emmanuel Adebayor's second-half strike meant that Arsenal came out of the first leg with a slight advantage. Arsene Wenger's side have come good at the right time in the season and by securing a draw at Estadio El Madrigal, they've given themselves a brilliant opportunity to progress to the semi-finals. The only downside is that a number of key players will now be missing through injury, with probably the biggest loss of all being Manuel Almunia. Villarreal will probably score at the Emirates but Arsenal have so much pace and creativity in their forward line that goals shouldn't be a problem.

Second-leg prediction: Arsenal 2-1 Villarreal (3-2 on aggregate)