To the strains of Thunderstruck by AC/DC, a spectacular firework display lit up the night sky above St. James' Park before kick-off - and it was a lightning start from the Magpies, who forced Barcelona back in the opening exchanges.
It took until the 16th minute for that early pressure to lead to a clear opportunity, which came when Jacob Ramsey - back in the side after serving a one-match ban at the weekend - prodded the ball through to Anthony Elanga. His shot was saved by Joan García and the flag went up against the Newcastle winger, but replays suggested he was onside.
Lamine Yamal saw an effort from a tight angle pushed onto the side netting by Aaron Ramsdale but United continued to look threatening and after a nicely worked move on the right, Elanga sent over a deep cross which William Osula headed over the bar.
In the 33rd minute, Elanga popped up again as he cut inside and let fly with a low drive which was gathered by García.
Fermín López cracked in a shot, which Ramsdale fielded, after Kieran Trippier lost his footing inside his own half, but moments later Elanga beat his man on the right and flashed a low centre across goal.
The second half took some time to truly warm up but Barnes almost set the game alight as he jinked inside and shot, but goalkeeper García was equal to it.
Robert Lewandowski had for the most part been kept quiet by Dan Burn, but came within a whisker of giving Barça the lead when Raphinha's wonderful touch was followed by a dangerous low ball, but the veteran striker prodded wide at full stretch.
Eddie Howe immediately made a triple substitution, introducing Anthony Gordon, Tino Livramento and Jacob Murphy in place of Osula, Trippier and Elanga, and Murphy quickly had an opportunity, meeting Lewis Hall's deep cross at the far post but firing over.
Illness meant Gordon, the Champions League's second-top scorer so far this term, was only fit enough to begin on the bench - and United fans must have felt sick after their celebrations were cut short when they thought Joelinton had put their side in front. Gordon broke on the right and squared to Murphy, who played in Barnes. His shot bounced back off the far post with García beaten, but Joelinton forced home the rebound. Alas, the Brazilian was offside.
Ramsey saw a strike deflected over in the 80th minute before, with five minutes left, came Barnes' big moment. Murphy got to the byline and sent over an inviting cross which Barnes side-footed home for his sixth of this season's competition.
Howe had described this as the biggest game in the club's recent history. They look set to go into next weekend's second leg with the tie narrowly in their favour.
**Newcastle United:** Aaron Ramsdale, Kieran Trippier (c) (Tino Livramento 67), Lewis Hall, Joelinton, Sandro Tonali, Harvey Barnes, Malick Thiaw, William Osula (Anthony Gordon 67), Anthony Elanga (Jacob Murphy 67), Dan Burn, Jacob Ramsey
**Subs not used:** Nick Pope, John Ruddy, Aidan Harris, Sven Botman, Yoane Wissa, Anthony Gordon, Tino Livramento, Jacob Murphy, Nick Woltemade, Joe Willock, Alex Murphy, Sean Neave