Newcastle thought they had secured the advantage heading to Spain, but a late penalty from Lamine Yamal ensured the tie remained level.
The Magpies looked set to head to Barcelona with the lead, with a late goal from Harvey Barnes as St James’ Park erupted.
However, late into added time, Malick Thiaw brought Dani Olmo down in the penalty area, and Yamal would step up and send Aaron Ramsdale the wrong way.
Anthony Gordon and Jacob Murphy were named on the bench following some minor issues last week.
Newcastle nearly made the perfect start as Sandro Tonali’s header was fumbled by Joan Garcia and rolled goalwards.
Luckily for the Spanish shot stopper, Pau Cubarsi was there to hook the ball away from danger.
Newcastle kept the pressure on with chances from William Osula and Anthony Elanga, but Barcelona held firm.
They were nearly rewarded for their hard defensive work when Raphinha’s cross rolled past Aaron Ramsdale’s post after taking a touch from Dan Burn.
Both teams began to settle into the contest as the first half wore on, but Elanga’s dangerous cross was inches away from finding Osula inside the box.
The match continued to be a tight battle between the two until Elanga breezed past his man and looked to pick out Harvey Barnes at the back post.
However, his cross lacked direction and timing, which made it easy for Garcia to come and collect.
Robert Lewandowski nearly made the Magpies rue their missed chances as his first effort of the game whistled past the post.
With the game heading into the final quarter hour, Joelinton put the ball into the back of Barca’s net, but he was clearly offside.
As time was running out, Newcastle’s pressure finally paid off as Barnes was on cue to turn home substitute Murphy’s cross, sending the home fans into delirium.
The atmosphere grew tense as the clock ticked down.
Deep into stoppage time, Thiaw brought down Olmo, and the referee immediately pointed to the spot.
Yamal shouldered the responsibility, and he calmly sent Ramsdale the wrong way, giving Barcelona an important goal.
Eddie Howe’s side will have to head to Spain and win, something they have only managed once in the six meetings between the clubs.
Newcastle will now turn their focus to Stamford Bridge on Saturday, a ground they haven’t won at in the Premier League since 2011.
Barcelona host Sevilla in La Liga on Sunday, before the second leg in Catalonia on Wednesday, which kicks off at 5:45 pm.
