Chelsea secured their spot in the semi-finals after seeing off Slavia Praha, while Arsenal, Valencia and Eintracht Frankfurt secured progression on Thursday evening.
Chelsea 4-3 Slavia Praha
After winning 1-0 in the first leg, Chelsea ran riot as goals from Pedro, Olivier Giroud and a Simon Dele gave the hosts a 3-0 lead inside 20 minutes.
Tomas Soucek reduced the deficit in the 25th minute, before Pedro netted the Blues' fourth two minutes later.
Petr Sevcik bagged two goals in the second half make it 4-3 on the night after 54 minutes, but the London outfit were able to see out the remaining stages to win 5-3 on aggregate.
Napoli 0-1 Arsenal
The Gunners advance to the semi-finals of the tournament following a slender second-leg win in Naples.
Alexander Lacazette opened the scoring for the visitors after 36 minutes to make it 3-0 on aggregate.
Valencia 2-0 Villarreal
Valencia are the only LaLiga side left in the competition following a 5-1 aggregate victory over Villarreal.
Following a 3-1 first-leg victory, the home side broke the deadlock 13 minutes into the first half thanks to a strike from Marcelino.
Valencia got their second goal 10 minutes into the second half, with Dani Parejo firing past Andres Fernandez.
Eintracht Frankfurt 2-0 Benfica
Eintracht Frankfurt advanced to the semi-finals after defeating Benfica 2-0 in the second leg.
The first leg ended 4-2 in favour of Benfica, but goals from Filip Kostic and Sebastian Rode saw the Bundesliga outfit advance on the away goals rule.
Frankfurt will now face Chelsea in the semi-finals, while Arsenal take on Valencia.