Cristiano Ronaldo netted a last-minute winner as Real Madrid defeated Manchester City 3-2 in an eagerly-anticipated UEFA Champions League Group D clash at the Bernabeu Stadium.
City looked like it might snatch a clash in which it had been outplayed when Aleksandar Kolarov struck late on.
But Madrid responded to the delight of the Bernabeu as Karim Benzema levelled and Ronaldo won it 3-2 at the death.
City had taken a 1-0 lead against the run of play through substitute Edin Dzeko in the second half but Marcelo quickly cancelled out the strike.
There was late drama in the other Group D game where Robert Lewandowski's 87th-minute goal gave Borussia Dortmund a 1-0 victory over Ajax.
Mats Hummels' missed second-half penalty looked like being costly for Jurgen Klopp's side but Lewandowski struck three minutes from time in front of a crowd of more than 80,000 at the Westfalenstadion.
Paris Saint-Germain made a convincing start to its Group A campaign with a 4-1 victory over Dynamo Kiev at the Parc des Princes.
Carlo Ancelotti's men never looked back after establishing a three-goal lead inside 32 minutes, through Zlatan Ibrahimovic's penalty, Thiago Silva's close-range finish and Alex's right-foot blast from Clement Chantome's outswinging corner.
Although Miguel Veloso pulled a goal back four minutes from time, Javier Pastore wrapped up the scoring in injury-time as PSG ended an eight-year absence from European football's top club competition in style.
Porto won the other Group A match 2-0 away to Dinamo Zagreb.
Steven Defour put the seal on the win in injury-time after Luiz Gonzalez put the visitor in front four minutes before the break.
The win keeps Vitor Pereira's side unbeaten in all competitions in a run stretching back to a League Cup defeat at Benfica in March.
Arsenal got its campaign off to a winning start after coming from behind to beat Montpellier 2-1 in France.
Manager Arsene Wenger, serving the first of his three-game touchline UEFA ban, would have been fuming from the stands when captain Thomas Vermaelen gave away an early penalty, although replays suggested the foul was probably just outside the box.
However, the Premier League club - coached by assistant boss Steve Bould from the sidelines for the first time - responded magnificently and was soon level through a fine finish by Lukas Podolski.
Before the French side, making its Champions League debut after last season's brilliant Ligue 1 campaign, could recover, Arsenal swept ahead on 18 minutes through Gervinho.
The other Group B match saw Schalke open with victory in a closely-fought game against Olympiacos in Greece.
Benedikt Howedes headed the German side in front four minutes before half-time and, after Djamel Abdoun equalised, Klaas-Jan Huntelaar grabbed what proved to be the winner.
The Netherlands striker then missed a penalty but his side nevertheless made a winning start.
Malaga began its first ever Champions League campaign in perfect fashion as two stunning goals from Isco guided it to a 3-0 win over Zenit St Petersburg at La Rosaleda.
The game was barely three minutes old when the Spain Under-21 international bent a wonderful shot in off the inside of the post and the host was in dreamland when Javier Saviola slid home a second 10 minutes later.
Zenit then missed a host of opportunities to get back into the game with Roman Shirokov and Alexander Kerzhakov the main culprits and its miserable evening was rounded off when Isco thumped in a third from outside the area with 14 minutes remaining.
The other Group C match saw AC Milan's struggles continue in a 0-0 home draw against Anderlecht.