Atletico Madrid and Benfica head into half time level at 1-1 after Nico Gaitan cancelled out a Champions League debut goal from Angel Correa.
The Portuguese side were quick onto the attack, and they fired a warning shot in the eighth minute when Jonas skipped past two defenders and struck inches wide of Jan Oblak's goal.
Atletico soon settled into the game and they came close at the other end minutes later when Tiago Mendes gained possession in the danger zone and let fly, his deflected effort rebounding wide for a corner.
Benfica were on the front foot again in the 16th minute as Goncalo Guedes caught Oblak off his line and attempted a lob, but former Chelsea man Filipe Luis was on hand to hack it away.
The home side took the lead in the 24th minute courtesy of a strike from Correa, the youngster drilling the ball home after Antoine Griezmann nodded it into his path.
Atletico looked odds-on to take a narrow lead into the break, but Gaitan turned up at the back post to smash home Nelson Semedo's cross with nine minutes of the first half remaining to give both sides everything to play for in the second period.
