Borussia Dortmund got their Champions League campaign off to a perfect start against Arsenal, while Liverpool needed an injury-time penalty to beat Bulgarian minnows Ludogorets Razgrad on their return to competition.
A goal in each half for Borussia Dortmund sealed a 2-0 win over Arsenal in their first game of the group stage.
Real Madrid thrashed Basel but there was a shocking defeat for their city rivals Atletico away at Olympiakos. Juventus secured victory at home to Swedish debutants Malmo with Monaco celebrating their first season back among the elite with a win over Bayer Leverkusen.
Arsenal endured a chastening start to their campaign after being overwhelmed by Borussia Dortmund at Signal Iduna Park.
Ciro Immobile and Pierre-Emerick Aubameyang struck moments either side of halftime and the German club would have been more emphatic victors than 2-0 but for the reflexes of Wojciech Szczesny and the Bundesliga club's wastefulness.
And for the second time in as many matches Danny Welbeck illustrated why his finishing is considered below par for a top forward as he missed a hat trick of good chances.
Steven Gerrard's stoppage time penalty kick proved to be the winner as Liverpool were pushed to the brink by Ludogorets.
Steven Gerrard converted a penalty in the third minute of stoppage time to earn Liverpool a 2-1 victory over Ludogorets Razgrad after a frantic finish to the Group B game at Anfield.
Dani Abalo's goal in the opening seconds of stoppage time canceled out Mario Balotelli's 82nd-minute strike and looked likely to earn a draw for the Bulgarian minnows, who were making their debut in the competition's group stage.
But goalkeeper Milan Borjan brought down substitute Fabio Borini moments later and Gerrard slotted home the spot kick to complete a successful return to Europe's elite competition for Liverpool after five years out.
Real Madrid thumped Basel to begin their Champions League campaign 5-1, led by goals from Karim Benzema, Gareth Bale, Cristiano Ronaldo and James Rodriguez.
Real Madrid opened the defence of their title with a 5-1 mauling of Baselin Group B at the Santiago Bernabeu as stars Gareth Bale, Cristiano Ronaldo and James Rodrguez all found the target in seven first-half minutes after an own-goal from Marek Suchy got the ball rolling.
The second goal came on the half hour as Luka Modric produced a sublime pass with the outside of his right foot which went into the path of Bale on the left. The Welshman knocked the ball over the goalkeeper on the half-volley and then went round him to supply his own finish.
Just a minute later, the former Tottenham duo were involved in the third with Modric again using the outside of the right foot to find Bale, who this time was on the opposite wing. He squared the ball across the front of goal and Ronaldo was left with a simple tap-in.
Real were absolutely rampant now and it was 4-0 eight minutes before the break as Ronaldo and Benzema exchanged passes for the Frenchman to have a shot from just inside the box. His shot deflected off Samuel and Tomas Vaclik did brilliantly to get a hand to it, but Rodriguez was there to turn home the rebound.
Derlis Gonzalez grabbed one back for Basel, but Karim Benzema completed the scoring with 10 minutes remaining.
A goal and an assist from Ibrahim Afellay led Olympiakos to a first group stage game triumph over Atletico Madrid.
Atletico Madrid slipped to a surprise 3-2 defeat to Olympiakos in a disappointing return to the Champions League for last season's finalists.
Atletico fell behind in the 13th minute of the Group A match when defender Arthur Masuaku aimed a left-footed drive past goalkeeper Jan Oblak, who was making his debut for the Spanish club.
Striker Kostas Mitroglou unselfishly left the ball to Imbrahim Afellay, who made it 2-0 in the 31st minute. But Mario Mandzukic pulled a goal back before the break, left unmarked to head in a cross from Cristian Ansaldi.
Mitroglou scored what proved to be the winner in the 73rd minute, turning on the ball to beat Oblak, before substitute Antoine Griezmann found the net in the 86th minute for Atletico.
Carlos Tevez broke his goal-scoring drought with two, which were enough to secure three points for Juventus against Malmo in their Champions League opener.
Carlos Tevez broke his Champions League duck as he scored twice to lead Juventus to a hard-fought 2-0 victory at home against Malmo in their opening Group A fixture.
Juventus struggled at times before Tevez broke the deadlock in the 59th minute, following good interplay with Kwadwo Asamoah. Tevez then sealed the result in stoppage time with a well-placed free kick that sailed into the top corner.
They were the Argentina forward's first Champions League goals in more than five years.
Despite summer transfers, AS Monaco were triumphant over German side Bayer Leverkusen, courtesy of Joao Mourinho's finish.
Joao Moutinho scored against the run of the play as Monaco recovered from a terrible start to beat Bayer Leverkusen 1-0 in their Group C opener.
Moutinho broke the deadlock in the 61st minute from former Leverkusen striker Dimitar Berbatov's assist as the Bundesliga leaders were made to pay for their profligacy.
Two first-half goals from Zenit St Petersburg were enough to secure a 2-0 first group stage game victory over Benfica.
Hulk and Axel Witsel scored first-half goals to give Zenit St Petersburga 2-0 win against 10-man Benfica in their opening Group C game.
Hulk put Zenit ahead in the fifth minute. The Brazilian striker was unmarked on the right when he received a pass from Oleg Shatov and curled the ball past Artur.
The Benfica goalkeeper was sent off in the 18th minute after obstructing Danny, and Witsel extended Zenit's lead with a glancing header at the front post four minutes later.
Burak Yılmaz scored a stoppage time equaliser for Galatasaray in a 1-1 draw against Anderlecht.
Burak Yilmaz scored in the first minute of stoppage time to help Galatasaray salvage a 1-1 draw with Anderlecht in Istanbul in Group D.
Yilmaz spared the hosts the embarrassment of defeat in the first round, netting in the 91st minute after Aurelien Chedjou rounded defenders before feeding a deft pass into the Turkish international's path.
After a goalless first half, Anderlecht's Dennis Praet had knocked in a low shot from the edge of the box in the 52nd minute.
Anderlecht's U.S. international Sacha Kljestan entered the game as a substitute in the second half.
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