Luis Suarez scored a scintillating double and the returning Lionel Messi set up the winner as Barcelona came from behind to beat Inter Milan in a thrilling contest at Camp Nou on Wednesday.
Lautaro Martinez fired Inter ahead after just two minutes and Antonio Conte's side, mean in defence and ruthless on the break, looked capable of pulling off an historic victory in Group F.
But Suarez broke down the Italians' determined back-line with a stunning volley just before the hour and then finished off a weaving Messi run in the 84th minute to complete a pulsating 2-1 win.
Inter had never beaten Barcelona away from home in the Champions League but were the better side for long spells, particularly in the first half when they should have added to their one-goal lead.
Instead, Barca's deadly duo came up trumps again, Suarez breaking through just as the hosts looked to be running out of ideas before Messi, back from injury, teed up his partner for the decisive second.
Inter play Juventus at home on Sunday, sitting top of Serie A after winning all of their six games so far and on this evidence, they could go far in Europe too.
Barcelona will be wary of the return fixture at the San Siro in December, which could yet decide who wins this group.
For Ernesto Valverde's team, a hard-fought victory, combined with Messi's return, will come as a welcome boost to morale and momentum after consecutive victories in La Liga steadied the ship following a bumpy start.
While they had their star striker back for only his second start of the season, Inter were without theirs, Romelu Lukaku ruled out with a thigh strain.
The first half was an engrossing battle of control against counter-attack as Barcelona had 67 per cent of the ball but Inter more of the clear-cut chances.
The pattern was set by Inter scoring early, after 122 seconds, as Gerard Pique was pulled out of position and Martinez sprinted into the gap, holding off Clement Lenglet before finishing inside the far post.
For half an hour, Barcelona played well, switching the ball from one side to the other in an attempt to dislodge the dogged Inter defence.
But the threat of their opponents on the break was always lurking and as the half wore on, Inter looked increasingly likely to grab a second.
Antonio Candreva scored but was ruled offside, Nicolo Barella would have but Nelson Semedo made a last-ditch block while Martinez and Alexis Sanchez both went close, the former drawing an excellent save from Marc-Andre ter Stegen.