Paris Saint-Germain Germain 2-1 Juventus
Paris Saint-Germain enjoyed a winning start in Group H after edging Juventus 2-1 at Parc des Princes.
Kylian Mbappe gave PSG an early lead and doubled their advantage midway through the first stanza for his brace as well.
Weston McKennie pulled a goal back for the Old Lady eight minutes from the half-time break.
Celtic 0-3 Real Madrid
Real Madrid got their title defence underway in style after thrashing Celtic 3-0 in Group F at Celtic Park.
Madrid were kept at bay in the first stanza and we spared by the woodwork from going behind on 21 minutes from a strike by Callum McGregor.
Vinicius Junior finally got the breakthrough for Los Blancos 11 minutes into the second-half and Luka Modric gave them a two-goal cushion on the hour-mark.
Eden Hazard put the game beyond doubt for Carlo Ancelotti's charges 13 minutes before full-time.
Here are Real Madrid's biggest earners this season, per Capology
Sevilla 0-4 Manchester City
Manchester City ran riot in their Group G opener after drubbing Sevilla 4-0 at Estadio Ramon Sanchez Pizjuan.
Erling Haaland opened the scoring for City on 20 minutes, Phil Foden settled the nerves with the second goal just before the hour-mark.
The Norwegian put the game to bed for Pep Guardiola's charges seven minutes later and grabbed his brace in the process.
Ruben Dias rubbed salt into Sevilla wounds in stoppage time as the Citizens ran riot.
RB Salzburg 1-1 AC Milan
AC Milan and Salzburg opened their Group E campaign with a point apiece after a 1-1 draw at Red Bull Arena in Salzburg.
Noah Okafor broke the deadlock for Salzburg just before the half-hour mark but Alexis Saelemaekers levelled matters for Milan five minutes before the half-time interval.
Benfica 2-0 Maccabi Haifa
Benfica enjoyed a perfect start in Group H after beating Maccabi Haifa 2-0 at Estadio da Luz.
Following a goalless first stanza, Rafa Silva eventually broke the deadlock for Benfica early in the second stanza and Alejandro Grimaldo doubled their lead six minutes before the hour-mark.
RB Leipzig 1-4 Shakhtar Donetsk
RB Leipzig suffered a 4-1 defeat to Shakhtar Donetsk in their opening match of Group F Red Bull Arena in Leipzig.
Marian Shved handed Shakhtar the lead on 16 minutes and Mohamed Simakan levelled matters for Leipzig just before the hour-mark.
Shved restored the lead for the visitors a minute later and got his brace.
Mykhailo Mudryk gave Shakhtar a two-goal buffer 14 minutes before time and Lassina Traore sealed the deal for the visitors five minutes before time.