Man Utd v Porto
Reigning champions Manchester United have faced Porto three times in the Champions League and lost twice, yet the Red Devils were relatively relieved when the Portuguese champions followed them out of the bowl during the draw.
With Cristiano Ronaldo and Nani in the squad and Sir Alex Ferguson's former No2, Carlos Quiroz, now managing the Portugal national team, United have access to in-depth information on Iberian football.
And having seen Arsenal demolish the Dragons 4-0 at the Emirates in the group stages, Ferguson will be confident he can balance the books in their fourth European encounter.
After going 14 games without conceding a goal, United have looked shaky in defence of late. And Rio Ferdinand and Nemanja Vidic will need to be at their best to keep Argentine Lisandro Lopez at bay.
The 26-year-old has scored six goals in seven games for coach Jesualdo Ferreira in Europe's elite competition and will be looking to add to his four goals away from the Estadio do Dragâo on Tuesday at Old Trafford.
United looked assured in the 2-0 second leg against Inter Milan, tempering the Nerazzuri attacks with threatening counters. Brazil's Anderson is a former Dragon and would relish the opportunity to play, but with Ferguson determined not to concede an away goal, he may opt for a more defensive-minded midfielder, such as Michael Carrick or Darren Fletcher.
Barcelona v Bayern
Barcelona striker Thierry Henry recently described his compatriot Franck Ribery as "Bayern's Lionel Messi" and if the two flair players turn up this has the potential to be the game of the tournament.
The two sides may have produced just four goals in their only other Champions League double-header, but an entirely different affair can be expected this time round: Bayern humiliated Sporting 12-1 on aggregate last month while Barca put five past French champions Lyon at the Nou Camp.
Bavarians' coach Jurgen Klinsmann has watched Bayern grow this season having missed out on elite action last year and, with a wide array of options in attack, the German side can produce goals from all across the field. In their 7-1 win over Sporting at the Allianz Arena, Bayern celebrated six different scorers and saw Lukas Podolski – the German striker who is far from first choice in attack – net a brace.
Likewise, in Henry, Messi and Samuel Eto'o, Barcelona have one of the most terrific attacking trios in world football. Twenty-one-year-old Messi has produced several moments of mercurial magic in his career already, but added yet another last week.
Having already opened the scoring for Argentina in their 4-0 rout of Venezuela, the Barcelona playmaker produced a dribble so good that coach Diego Maradona said that, had it ended in a goal, the home fans would have been obliged to leave the stadium and pay to get in again.
Liverpool v Chelsea
Undoubtedly the tie of the quarter-finals, both sets of fans released audible moans of irritation when the draw was announced last month.
The pair have met in Europe every season for the past five years, with Reds boss Rafa Benitez boasting an unblemished record until John Arne Riise headed into his own net last year to send Chelsea to the final in Moscow.
Liverpool, who looked fatigued and unfit for a title race in February, have enjoyed a renaissance since their last European outing.
After crushing Juande Ramos' Real Madrid 4-0 at Anfield, the Reds went on to score nine goals in two games in victories against Man United (4-1) and league high-flyers Aston Villa (5-0) to produce a march back up the table. Chelsea meanwhile, had a run of six successive league wins ended on their last outing at Tottenham.
The loss marked the first defeat under temporary coach Guus Hiddink, who joined the club in February following the dismissal of Luiz Felipe Scolari.
Scolari's contract was terminated just eight days after the Blues suffered a 2-0 defeat at the hands of their Red rivals.
However, Hiddink's record against Benitez is also little to behold: The last time the two coaches squared up, the Dutchman saw his PSV Eindhoven side lose 3-0 at home and then 1-0 away in the 2007 quarter-finals.
He'll be looking to rectify those results when the old foes battle on Tuesday.
Villarreal v Arsenal
Nicknamed "The Yellow Submarines", Spanish outfit Villarreal, who were beaten in the semi-finals of the Champions League by Arsenal in 2006, have refused to 'Let It Be' and will be looking to do 'Every Little Thing' to exact revenge when the two sides meet again at El Madrigal on Tuesday.
The La Liga side will want to finish the tie in Spain as manager Manuel Pellegrini is only too aware that his men often suffer from travel sickness having failed to win away from Castellon in three attempts during the group stages.
Despite smashing six past Aalborg in the home leg, they could only manage a 2-2 draw two weeks later at the Energi Nord Arena. Likewise, at El Madrigal, the home team beat Celtic 1-0, but slipped to a 2-0 reverse at Parkhead. A sign that such form may be turning, however, came in Athens when they held on for a 2-1 win at Panathinaikos.
Villarreal are the only remaining side to have never reached a Champions League final and they will have to be frugal in defence against Arsenal if they are to advance to the semis.
The Gunners have been in scintillating league form of late, netting 15 goals in their last five games. Yet, in Europe, Arsene Wenger's men had to rely on a penalty shoot-out miss from Roma defender Max Tonetto to progress to the quarter-finals. Arsenal are unbeaten in 21 league games and are reaping the benefits of having captain Cesc Fabregas and England winger Theo Walcott back after long-term injuries.