Liverpool beat Lille 2-1 on Tuesday to maintain their perfect record in this season's Champions League and clinch qualification for the last 16, while Barcelona produced a stunning comeback to beat Benfica 5-4 in a classic to secure their own place.
The Anfield side are the only team with a maximum 21 points from seven matches in this new, expanded Champions League and they now know they will skip next month's play-offs and head straight to the last 16 in March.
Mohamed Salah ran clear to give Liverpool the lead at home to a Lille team who have also impressed this season, and the visitors appeared in trouble when they had Aissa Mandi sent off just before the hour mark.
Jonathan David swept in an equaliser for Lille, but Harvey Elliott's shot took a wicked deflection on its way in to give Liverpool the points.
"We're happy that we are top eight. That's the only thing that tells me something, because this league table doesn't tell you anything," said Slot when asked about being through to the last 16.
The biggest drama on the night, however, came in the rain in Lisbon, where Barcelona trailed 4-2 with 12 minutes of the 90 remaining, but somehow recovered to win 5-4.
Greek striker Vangelis Pavlidis scored a hat-trick in the first half-hour for Benfica, including a penalty, while Robert Lewandowski netted from the spot for Barca, who were 3-1 down at the interval.
Raphinha pulled it back to 3-2 when a clearance by the goalkeeper ricocheted back off the Brazilian's head and in, but a Ronald Araujo own goal midway through the second half appeared to have secured the win for the Portuguese side.
However, another Lewandowski penalty on 78 minutes gave Barcelona renewed hope, and Eric Garcia headed in the equaliser on 86 minutes, before Raphinha ran away to settle an incredible game.
"The mentality of the team, they always believe in themselves and this was unbelievable to see," said Barcelona coach Hansi Flick.
The Catalans are second with six wins out of seven, and will finish in the top eight to go straight to the last 16. Benfica, with 10 points, must still sweat to reach the play-off round.
ALVAREZ GIVES ATLETICO VICTORY
Elsewhere, Atletico Madrid are third on 15 points and certain to at least be in the play-offs after a Julian Alvarez brace secured a 2-1 home victory over Bayer Leverkusen in a game both teams finished with 10 men.
Atletico had Pablo Barrios sent off midway through the first half, and Piero Hincapie then put Leverkusen ahead just before the break.
Argentina star Alvarez levelled seven minutes into the second half, and Hincapie was sent off for the Germans before another Alvarez goal won it for the home side in the last minute as they climbed above Leverkusen.
Last season's Europa League winners Atalanta are also guaranteed at least a play-off place after crushing Sturm Graz of Austria 5-0.
Mateo Retegui, Mario Pasalic, Charles De Ketelaere, Ademola Lookman and Marco Brescianini all scored for the Italians.
Monaco got back to winning ways after some disappointing results had seen their campaign stall, as Wilfried Singo's early goal proved enough for them to beat Aston Villa 1-0.
Both teams are set to progress to the knockout phase and both could still finish in the top eight.
Last season's runners-up Borussia Dortmund should also be fine despite a 2-1 defeat away to Bologna, as substitutes Thijs Dallinga and Samuel Iling-Junior scored a minute apart in the second half after Serhou Guirassy's early penalty had put the Germans in front.
Club Brugge held Juventus to a 0-0 draw in Belgium as that duo both look set to go through to the play-offs at least, while PSV Eindhoven are poised to advance following a 3-2 win at Red Star Belgrade.
PSV led 3-0 at the break thanks to a Luuk de Jong double and a Ryan Flamingo strike, but the latter was sent off early in the second half and Red Star pulled goals back courtesy of Cherif Ndiaye and Nasser Djiga.
VfB Stuttgart maintained their hopes of reaching the play-offs with a 3-1 win away to Slovan Bratislava, who have lost every game.
Jamie Leweling bagged a brace for Stuttgart and Fabian Rieder sealed their victory after Idjessi Metsoko had pulled one back.