Luis Suarez grabbed a brace as Barcelona came from a goal down to beat Atletico Madrid 2-1 at the Nou Camp.
Fernando Torres had given Atletico Madrid the lead before he was sent in the first half.
Both teams will meet again for the return leg at the Vicente Calderon.
Barcelona had the first attempt on goal in the fifth minute through Lionel Messi but his left foot drive narrowly missed the target.
Messi came close again in the 13th minute off a Jordi Alba cross but shot wide.
In the 19th minute Neymar had the game’s first real chance but his header went just over the bar.
Antoine Griezman tried a strike outside Barcelona’s 18-yard box which went inches off the post.
Fernando Torres opened the scoring in the 25th minute, sliding the ball beneath Ter Stegen following a Carrasco pass.
Ter Stegen made a very good save in the 32nd minute to prevent Griezman’s left-foot shot.
Torres was sent off in the 36th minute for a second bookable offence for a foul on Sergio Busquet.
In the 41st minute Javier Mascherano struck a long range strike but Oblak made a simple catch.
Neymar tried a left-foot drive in the second minute of added time which went wide.
Mascherano made a good block in the 47th minute off Saul’s header which was on target.
Messi almost made it 1-1 with a bicycle kick which went inches wide.
In the 51st minute Neymar saw his right-foot curler come off the cross bar.
Atletico made their first change in the 53rd minute with Augusto Fernandez replacing Carrasco.
On 55 minutes, Neymar headed Rakitic’s cross straight at Oblak.
A minute later Messi’s shot was stopped by Oblak with Neymar failing to pounce on the rebound before it was cleared away.
Another good work from Neymar in the 62nd minute saw his curler miss the target again.
Barcelona’s persistent pressure finally paid off when Luis Suarez tapped in Alba’s cross in the 63rd minute.
Suarez made it 2-1 in the 74th minute, heading in Dani Alves cross.
In the 85th minute Messi made a drive towards Atletico’s area and was brought down but the referee waved play on.
At the Allianz Arena Bayern Munich could only manage a 1-0 win against Benfica.
The only goal of the game was scored by Arturo Vidal in the second minute with a header.