Barcelona twice fought back from two goals down – and two Wojciech Szczesny howlers – to snatch a dramatic victory at Benfica.
The hosts made a dream start as Greek striker Vangelis Pavlidis hit a 30-minute hat-trick, helped by two mistakes from Polish keeper Szczesny, while Robert Lewandowski replied from the penalty spot for the Spanish side.
Goals for Raphinha and Lewandowski, either side of an Ronald Araujo own goal, then left Barca one behind at 4-3.
But Eric Garcia headed home a late equaliser and in the 96th minute, just after Szczesny had made a fine block from Angel di Maria and Benfica were denied a penalty, Raphinha broke away and slotted past Anatoliy Trubin to leave the home crowd stunned.
It was a sensational comeback from Barca, who clinched their place in the last 16 with their 18-point tally.
Benfica will wonder what happened, having raced into an early lead when full-back Alvaro Carreras got in behind Jules Kounde and crossed for Pavlidis to emphatically thump the ball home.
Barcelona drew level from the penalty spot through Lewandowski after Tomas Araujo was judged to have stood on the foot of Alejandro Balde.
Gavi forced Trubin into a smart save before Ronald Araujo headed over from a corner.
Then followed Szczesny’s gaffes.
The former Arsenal and Juventus stopper – making his first Champions League start for the club after coming out of retirement in October – raced out of his goal in an attempt to clear a long ball but succeeded only in colliding with team-mate Balde, leaving Pavlidis unchallenged to slot into the empty net.
Szczesny then raced off his line again, this time bringing down Benfica winger Kerem Aktürkoglu. Pavlidis coolly converted from the penalty spot to wrap up a superb treble.
Early in the second half Kounde mis-hit a back-post effort that would have got the visitors back in the game, while Fredrik Aursnes took too many touches when through on goal.
Another bizarre moment led to Raphinha’s first goal in the 64th minute as Trubin’s attempted clearance downfield hit the head of the Brazilian forward and bounced back over him and into the goal.
But Benfica’s two-goal cushion was restored four minutes later when Araujo sliced Andreas Schjelderup’s cross into his own net.
Lewandowski responded again from the penalty spot to set up a thrilling finale.
Garcia headed home to make it 4-4 and it seemed both sides would have to settle for a share of the spoils until Raphinha’s winner.
