Atletico Madrid and Porto played out an eventful stoppage-time on Wednesday, becoming just the second Champions League match to see three goals scored in the 90th minute or later.
The LaLiga side took the lead in the 91st minute through Mario Hermoso, who then handled in the box as Porto looked to have snatched a point when Mateus Uribe fired home the resulting penalty.
However, substitute Antoine Griezmann nodded in a stunning winner in the 11th minute of stoppage-time to send the home fans into raptures and give his side three points.
Griezmann's goal made the Champions League game only the second to feature three 90th-minute goals, after a match between the same two teams in December of last year, when Atletico ran out 3-1 winners.
The LaLiga side's late victory gets them off to a great start as they look to go further than they managed in last season's competition when they were knocked out at the quarter-final stage by Manchester City.
Porto will have to pick themselves up as they attempt to reach the knockout stages, with Club Brugge defeating Bayer Leverkusen 1-0 in the other Group B clash on matchday one.