Ancelotti sacked by Napoli
Napoli made sure of its progress by trouncing Genk 4-0 in Italy with Arkadisuz Milik scoring a first-half hat-trick, the third goal coming from the penalty spot.
Dries Mertens converted another spot-kick in the second half to seal the win, but the Italian side still sacked coach Carlo Ancelotti in the wake of the game.
There was high drama in Group H as Valencia beat Ajax 1-0 in Amsterdam, Rodrigo Moreno's strike taking the Spaniards through to the last-16 at the expense of last season's semifinalists, and leaving its hosts stunned.
Ajax had again been impressive this season but was left to rue its inability to win either of its two matches against Chelsea, as Frank Lampard's team progressed in second place, a point ahead of the Dutch giant, thanks to a 2-1 victory against Lille.
Tammy Abraham and Cesar Azpilicueta netted first-half goals for Chelsea, who held on after
Loic Remy pulled one back for Lille. Chelsea, the 2012 Champions League winner, finishes level on points with Valencia but come second due to its inferior head-to-head record.
Fati makes history for Barcelona
Ajax drops into the Europa League along with Inter, as Antonio Conte's team contrived to lose 1-2 at home to a makeshift Barcelona.
A win would have taken Inter through, and it was fancied to get the result it required as Barcelona left out a host of senior players, including Lionel Messi, with top spot in Group F already secured. Carles Perez gave Barcelona the lead midway through the first half, but Romelu Lukaku fired in the equaliser.
Inter then missed chances to score a second and Ansu Fati showed it the way, the substitute netting an 86th-minute winner to stun the home side and become the youngest ever goalscorer in the Champions League at 17 years and 40 days.
That record had been held since 1997 by Ghana's Peter Ofori-Quaye.
"Seeing replays of Fati's goal hurt," said Inter coach Antonio Conte. "It's a goal that cut our legs from under us and killed us from all points of view.”
Barcelona coach Ernesto Valverde said, "There was a lot of newness because we also changed our system,"
Borussia Dortmund needed to better Inter's result and it did so, beating Slavia Prague 2-1 to progress in second.
Julian Brandt got their winner after Jadon Sancho's opener was cancelled out by Tomas Soucek, with Dortmund holding on after Julian Weigl was sent off.
Meanwhile, Lyon went through in dramatic fashion in Group G, coming from behind to draw 2-2 with RB Leipzig.
The Germans were two goals ahead at half-time thanks to two penalties, one scored by Emil Forsberg and the other by Timo Werner. However, Houssem Aouar's curler gave Lyon hope just after the break and Memphis Depay levelled matters with eight minutes left.
Leipzig wins the group, while the draw proved enough for Lyon to finish second because Zenit Saint Petersburg lost 0-3 to Benfica in Lisbon. Franco Cervi gave Benfica the lead before a Pizzi penalty and a Sardar Azmoun own goal, as the Portuguese side finish third.