Barcelona superstar Lionel Messi followed up his weekend hat-trick with two more goals as Ernesto Valverde's men swaggered past Juventus.
Lionel Messi netted a brilliant brace as Barcelona helped themselves to a dose of Champions League revenge with a dominant 3-0 Group D win over Juventus.
The Serie A champions beat Barca by the same scoreline in the quarter-finals last season before holding out for a second-leg stalemate at Camp Nou.
Barca have since lost Neymar to Paris Saint-Germain, but it was Juve's' most notable pre-season departure – Leonardo Bonucci's surprise switch to AC Milan – that loomed largest over this match as a once formidable defence was cut to ribbons in Giorgio Chiellini's injury absence.
Also, Paris Saint-Germain produced a classy display to comfortably beat Celtic 5-0 in their opening Champions League Group B game on Tuesday night.
Goals from PSG's star-studded trio of Neymar (20), Kylian Mbappe (34) and Edinson Cavani (40 pen) helped PSG on their way to a convincing win at Celtic Park before a Mikael Lustig own goal (82) and Cavani's second (85) condemned Celtic to their heaviest home defeat in European competition.
After a year away, Chelsea returned to the Champions League with a comfortable victory over Qarabag as two new signings found the net.
Davide Zappacosta and Tiemoue Bakayoko hit their first Chelsea goals as the Blues returned to the Champions League with a rampant 6-0 group-stage win over Qarabag at Stamford Bridge.
After a year away from European competition, the three points never looked in doubt for the Premier League champions after Pedro kicked off their Group C campaign with a fifth-minute goal.
A bizarre strike from full debutant Zappacosta followed before the interval, Cesar Azpilicueta added a third and there was still time for substitute Bakayoko and Michy Batshuayi to get in on the act.
Gurban Gurbanov's visitors - becoming the first side from Azerbaijan to play in the main draw of Europe's premier club competition - never threatened to spring a surprise and Thibaut Courtois will enjoy few easier outings this season.
This is a fourth straight win for Antonio Conte's men in all competitions but three points here were the bare minimum.
Manchester United opened their Champions League campaign with a comfortable 3-0 victory over Basel at Old Trafford on Tuesday evening.
United, who returned to Europe's elite club competition after a one-year absence after winning the Europa League last season, lost Paul Pogba to injury in the first half but his replacement, Marouane Fellaini, made an instant impact, opening the scoring in the 35th minute.
Romelu Lukaku extended the hosts advantage in the 53rd minute before substitute Marcus Rashford made the points safe on what was a comfortable night for Jose Mourinho's side.
In Germany, Bayern Munich got off to a winning start in the Champions League for the 14th successive season on Tuesday with a comfortable 3-0 victory over Group B opponents Anderlecht.
In other games, Roma were held to a pulsating draw by Atletico Madrid while Olympiacos and Benfica suffered home defeats against Sporting CP and CSKA Moscow respectively.