The visitors were stunned in the opening minute when Dwight Gayle fired home after a quick free kick from Jonjo Shelvey, before a looping header from Virgil van Dijk got Liverpool back on level terms in the 38th minute.
Liverpool started the second half on the front foot, and their pressure soon told, as Divock Origi's excellent finish from distance just before the hour mark put his side ahead, and Sadio Mane came off the bench to add some gloss to the scoreline with a near-carbon copy of Origi's finish in the closing stages.
The response to going behind so early on was excellent, and it was only a matter of time before Liverpool's dominance on the ball hammered out a route back into the game.
The first-minute Gayle strike could perhaps be seen as a microcosm of the unconscious drop in game management and focus since sealing the title a few weeks ago, as you certainly would not have seen Jurgen Klopp's side concede a goal like that earlier in the season.
Manager rating out of 10
7 -- It was a chance for Klopp to give some of his fringe players a run out and, despite a poor start, the second-string stamped their authority on proceedings and ground out a win they were excellent value for.
Player ratings (1-10; 10 = best, players introduced after 70 minutes get no rating)
GK Alisson, 6 -- Couldn't quite get enough on Gayle's strike to stop it nestling home, but not a mistake by any stretch of the imagination, and the Brazilian had a quiet 89 minutes after that.
DF Andy Robertson, 7 -- Never in any danger defensively and was a regular fixture in the opposition half as he looked to make things happen on the Liverpool left. There was a 12th Premier League assist of the season for the Scot when he cushioned a cross-field pass for Origi, on the way to Liverpool's second.
DF Virgil van Dijk, 7 -- Got his side back on level terms with an excellent looping header over Martin Dubravka, and forced a save from the Newcastle stopper in the second half with a decent effort. Had little work to do defensively, but mopped up everything he needed to.
DF Joe Gomez, 6 -- Caught flat-footed as Shelvey floated the ball over him for the opener, but the defender asserted himself on the game thereafter and didn't give a sniff to the Newcastle frontline.
DF Neco Williams, 6 -- The 19-year-old was unable to get in line with the rest of his back four in time for Shelvey's clipped ball in-behind for Newcastle's first-minute opener, but the Welshman stuck to his task and looked comfortable, before picking up an injury late on and being replaced by Trent Alexander-Arnold.
MF Naby Keita, 7 -- Finally starting to look like he's finding his feet in the Liverpool midfield, and looked the most likely to make something happen in response to the early opener, making some gliding runs into the Newcastle area. A decent showing came to an end in the 85th minute when he was replaced by Curtis Jones.
MF Giorginio Wijnaldum, 6 -- There was a moment of naivety when the Dutchman passed the ball back to Shelvey for a home free kick before his defence could adequately organise itself for the opener.
MF James Milner, 6 -- Kept things ticking over in typical Milner fashion; the 34-year-old is showing no signs of slowing down any time soon.
MF Alex Oxlade-Chamberlain, 6 -- Playing out wide, the former Arsenal man did well to find space on the right flank before floating in a cross for Van Dijk to head home the equaliser, and then had Dubravka scrambling shortly after with a fizzing shot that just evaded the angle between post and bar. Brought off for Roberto Firmino after 63 minutes.
MF Takumi Minamino, 6 -- Forced Dubravka into a decent save with a good effort from the edge of the box in the first half, and the former FC Salzburg man looked keen to make an impression on the final day of the season. Replaced by Mane for the final 27 minutes.
FW Divock Origi, 7 -- The striker went into this one without a goal in 23 appearances, but didn't look short of confidence when he shifted inside and fired a brilliant strike into the far corner to put his side ahead just before the hour. Withdrawn in the 64th minute for Salah.
Mohamed Salah, 6 -- Fired against the post with his first touch as he searched for his 20th Premier League goal of the season.
Sadio Mane, 7 -- Rounded the Liverpool season off in superb style with a lovely curling effort, after cutting inside the penalty area.
Roberto Firmino, 6 -- Knitted Liverpool's attacking play together in the final half-hour, and played the ball out wide for Mane on the way to Liverpool's third.
Trent Alexander-Arnold, N/R -- Slotted in at right back for the final five minutes.
Curtis Jones, N/R -- Some neat footwork in his short cameo.