Napoli and PSV exit.
Arsenal needed a late comeback to secure their place in the draw for the Europa League last 16 where they will be joined by Ajax Amsterdam, Manchester United, Milan and Rangers but Napoli and PSV Eindhoven crashed out on Thursday.
Pierre-Emerick Aubameyang's 87th-minute header secured Arsenal a 3-2 win over Benfica for a 4-3 aggregate victory, but the Premier League side had been staring at the exit door.
After the first leg, played in Rome because of COVID-19 restrictions, ended 1-1, Arsenal's home leg was played in Athens and all looked comfortable when Aubameyang scored early on.
Diogo Goncalvez curled home a free kick for Portuguese giants Benfica just before halftime, however, and when a terrible mistake by Arsenal midfielder Dani Ceballos allowed Rafa Silva to put Benfica 2-1 ahead just past the hour it looked grim for Arsenal.
Kieran Tierney fired home the equaliser, however, before Aubameyang headed in from close range to seal a dramatic win.
"It certainly keeps the season going, that's for sure," Arsenal manager Mikel Arteta, whose team are 11th in the Premier League, said.
"Today would have been really harsh after what had happened in the two legs to go out."
Milan squeezed past Red Star Belgrade on away goals after their tie ended 3-3 on aggregate following a 1-1 draw in the San Siro. Franck Kessie's penalty gave Milan the lead but Red Star hit back through Ben Nabouhane and pushed hard late on despite being reduced to 10 men.
Roma completed a 5-1 aggregate in over Braga while Manchester United also eased through after a 0-0 home draw against Real Sociedad, following a 4-0 first leg win.
Former winners Napoli bowed out despite a 2-1 victory at home to Spanish club Granada.
Having lost the first leg 2-0 they got a perfect start when Piotr Zielinski put them in front after three minutes.
But Angel Montoro levelled for Granada and although Fabian Ruiz struck again for the hosts on the hour, Granada held on for a 3-2 aggregate win to prolong their impressive European debut.
Tottenham Hotspur had reached the last 16 the night before but Leicester City failed to make it four English clubs in the draw as they lost 2-0 at home to Slavia Prague.
Goals by Lukas Provod and Abdallah Sima ensured it was a great night for the Czechs who celebrated with a video call to former player Thomas Soucek, now at West Ham United.
"There is a fantastic euphoria right now," Provod said.
"It was a hard match, but we never stopped believing that we would score a goal."
Ajax beat French club Lille 2-1 for a 4-2 aggregate win although it was tough examination for the Dutch side who needed a late goal by David Neres to calm their nerves.
Rivals PSV Eindhoven's hopes disappeared as they lost a thrilling tie 5-4 on aggregate against Olympiacos, despite winning 2-1 on the night.
Eran Zahavi's brace appeared to be sending PSV through on away goals but Ahmed Hassan fired home in the 88th minute to leave the hosts in despair.
Scottish Premier League leaders Rangers completed an astonishing 9-5 aggregate win over Belgian side Antwerp thanks to a 5-2 win in Glasgow.
Villarreal made it through with a 2-1 defeat of Salzburg for a 4-1 aggregate win while Shakhtar Donetsk and Dynamo Kiev advanced against Maccabi Tel Aviv and Bruges respectively.
Norwegians Molde caused a surprise by winning 2-0 in Hoffenheim to wrap up a 5-3 aggregate triumph and Bayer Leverkusen suffered a 6-3 aggregate defeat by Young Boys.