Real Madrid struck twice at the death to defeat Sporting CP, Borussia Dortmund registered their biggest European away win and Leicester City were impressive victors in Bruges.
Group C
Manchester City 4-0 Borussia Mönchengladbach
On target three times in the play-off first leg against Steaua Bucureşti, Sergio Agüero hit his second UEFA Champions League hat-trick of the season as City cruised home in the rearranged fixture.
Group E
Bayer Leverkusen 2-2 CSKA Moskva
CSKA retrieved a 2-0 deficit before half-time through Alan Dzagoev and Roman Eremenko.
Tottenham Hotspur 1-2 Monaco
Beaten 4-1 away from home by Tottenham in the UEFA Europa League group stage last term, Monaco gained a measure of revenge at Wembley thanks to Bernardo Silva and first-half substitute Thomas Lemar.
Group F
Real Madrid 2-1 Sporting CP
Cristiano Ronaldo seemed to have salvaged a point for Madrid with an 89th-minute free-kick that Rui Patrício could only tip onto his left-hand post and in, Bruno César having stunned the holders earlier in the second half. Yet there was still time for Álvaro Morata to nick all three points four minutes into added time.
Legia Warszawa 0-6 Borussia Dortmund
Legia’s first UEFA Champions League group match since 1995/96 was a chastening one as Dortmund raced into a three-goal lead by the 17th minute. It got worse as six different BVB players found the back of the net.
Group G
Club Brugge 0-3 Leicester City
Marc Albrighton gave the debutants a dream start when he struck after a long throw was inadvertently flicked on by a Brugge defender. Riyad Mahrez then curled in a free-kick before converting a penalty just past the hour.
Porto 1-1 København
Otávio put the Dragons ahead on his UEFA Champions League bow with a rising shot, only for Andreas Cornelius to rescue a point for FCK.
Group H
Lyon 3-0 Dinamo Zagreb
Corentin Tolisso headed in the opener before the quarter-hour mark. Jordan Ferri and Maxwel Cornet moved the contest beyond Dinamo in the second period.
Juventus 0-0 Sevilla
Gonzalo Higuaín rattled the crossbar for the Serie A team, but the Bianconeri could not repeat their home victory over Sevilla from last season.