Liverpool's perfect record in this season's Champions League ended in a 3-2 loss to Fenerbahce in Turkey on Wednesday while Como hit nine away to Lens in an incredible performance as they equalled the biggest winning margin in the competition's history.
Elsewhere, Real Madrid produced another late comeback to maintain their perfect record in this season's league phase and there were away wins for Arsenal and Manchester City.
Liverpool went to Istanbul looking to make up for a loss to Arsenal in the Premier League at the weekend, and build on victories over Atletico Madrid, LASK and Villarreal in their previous European outings this season.
Trey Nyoni, 19, gave Liverpool the lead with his first senior goal, but Fenerbahce equalised through a deflected Mason Greenwood free-kick.
Sitting sixth in the Turkish Super Lig, Fenerbahce had already lost 6-0 at Aston Villa this season and came into this game with ex-Liverpool player Dirk Kuyt in charge of the team on an interim basis.
Alexander Isak headed Liverpool back in front on 69 minutes only for Englishman Archie Brown to grab a quick-fire leveller, before Vedat Muriqi won it for the home team.
"I think we've put ourselves in good positions, so that today if we lose this game it's not a chaos situation," said Isak. "We just need to get back to winning ways and if we win the next game, we are back to a really good position."
RECORDS
Como won 9-1 at Lens in France, as the side coached by Cesc Fabregas became just the third team since the launch of the modern UEFA Champions League in 1992 to win a game by an eight-goal margin.
Greek striker Anastasios Douvikas scored a hat-trick as the Serie A side made it three wins in four games in this season's league phase, two weeks after thumping Manchester United 4-1.
Liverpool hammered Besiktas 8-0 in the group stage in 2007 and Real Madrid won by the same scoreline against Malmo in 2015.
Como are just the second team to score nine in a game in the competition, after Bayern Munich beat Dinamo Zagreb 9-2 in 2024.
Douvikas got the first two goals for Como at the Stade Bollaert-Delelis, and Argentine star Nico Paz rifled in to make it 3-0 at halftime.
Lucas Da Cunha and Marc-Oliver Kempf both netted early in the second half, and Douvikas completed his hat-trick for 6-0 before Mattia Liberali got the seventh.
Ruben Aguilar pulled one back for Lens with a fine volley but Martin Baturina and Matteo Papaccioli capped an incredible night for the visitors.
They are fourth in the overall standings after four games with nine points, three points behind Paris Saint-Germain and Real Madrid, and one point behind Arsenal.
NONCHALANT
Madrid came from 3-1 down to beat Roma 4-3 in their last Champions League away outing, and this time they fought back to AEK Athens 3-2 in Greece.
Aboubakary Koita's early opener for the hosts was cancelled out by a nonchalant Jude Bellingham back-heel, but Stavros Pilios put AEK back in front on 75 minutes.
However, Kylian Mbappe levelled again with his 16th goal in all competitions this season, and Federico Valverde smashed in a stoppage-time winner before Koita was shown a red card at the end.
Noni Madueke and Viktor Gyokeres scored first-half goals as Arsenal won 2-1 away to Slavia Prague, for whom Wiktor Nowak grabbed a consolation.
"We have to value the fact that it's very difficult to win away from home. We've done it against a really tough opponent, as we expected," said Arsenal manager Mikel Arteta.
Manchester City are one of nine teams with nine points after Erling Haaland's late goal secured a 3-2 victory away to RB Leipzig.
City had led twice, first through a Castello Lukeba own goal and then an Enzo Fernandez finish, but the hosts had equalised on two occasions with Ridle Baku and Antonio Nusa on target.
Greek teenager Konstantinos Karetsas got the winner as Borussia Dortmund beat Real Betis 2-1 in Germany, while a Carlos Forbs strike secured a 2-1 victory for Club Brugge on their short trip to PSV Eindhoven.
Porto got their first points in this season's competition by thumping Napoli 4-1 in Portugal, while Viking Stavanger claimed a first win as they came from behind to beat Sabah of Azerbaijan, also 4-1.