Darwin Nunez gave the Reds the lead with a thumping finish after 10 minutes, collecting a pass from Trent Alexander-Arnold before drilling into the back of the net.
A second followed soon after when Mohamed Salah’s slick first-time flicked pass found Cody Gakpo, who brought it down and netted.
Newcastle then lost goalkeeper Nick Pope to a straight red card on 22 minutes after he handled outside the area under pressure from Salah.
The home side had opportunities to get back into the contest – most notably when Dan Burn headed against the crossbar – but Jürgen Klopp’s men condemned the Magpies to only their second top-flight loss of the season to close the gap on the top four.
Team news…
Liverpool made just one change from Monday’s win over Everton as Virgil van Dijk returned to the starting line-up, replacing Joel Matip.
Liverpool: Alisson, Alexander-Arnold, Gomez, Van Dijk, Robertson, Fabinho, Bajcetic (Milner, 58), Henderson (Elliott, 58), Nunez (Firmino, 58), Salah, Gakpo (Jota, 58).
Unused subs: Kelleher, Keita, Tsimikas, Matip, Phillips.
First half…
Newcastle took the early initiative in the contest and only a sterling save from Alisson Becker prevented them from taking the lead with four minutes on the clock.
Allan Saint-Maximin picked out an unmarked Miguel Almiron inside the area, who took a touch but was closed down quickly by Liverpool’s goalkeeper, who thwarted his eventual effort with a strong left glove.
However, the Reds’ first meaningful attack yielded a goal with 10 minutes gone.
Alexander-Arnold’s sublime pass over the top from deep on the right picked out Nunez, who brought the ball under control before rifling the bouncing ball beyond Pope from just inside the area.
The visitors’ start to proceedings got even better when Salah flicked a first-time pass into the path of Gakpo from just outside the box. The forward took it down and slotted in with aplomb to make it two in two.
Newcastle’s hopes of salvaging something took a further blow when Pope was shown a straight red. Alisson launched a trademark counter-attack to Salah from a set-piece from the Magpies. The hosts’ ’keeper raced from his line to intercept, but handled the ball after initially getting his head to it.
Martin Dubravka assumed the gloves for Eddie Howe’s team – and immediately had to keep out a header from Gakpo following an Alexander-Arnold delivery.
At the other end, Saint-Maximin created an opportunity out of nothing with some silky footwork inside the area, resulting in a shot Alisson pushed against the crossbar and over.
Newcastle then demonstrated once more the outcome was far from certain when Burn rattled the woodwork with a firm header from a corner before the break.
Second half…
The opening stanza of the second period saw Liverpool dominate the ball, but Newcastle fashion the first chance when Alexander Isak shot wide on the swivel after being picked out by Saint-Maximin’s low centre.
Then, another set-piece yielded an opportunity for Fabian Schar, who headed back across goal and wide from a corner.
At the other end, a counter from a home-team free-kick resulted in Nunez having a low shot tipped around the post by Dubravka.
That incident preceded a quadruple change by the Reds, who sent Diogo Jota, Roberto Firmino, Harvey Elliott and James Milner into the action in place of Nunez, Gakpo, Stefan Bajcetic and Jordan Henderson.
It was Jota and Firmino who combined for the game’s next chance, which the former lashed across goal from an angle.
Elliott then tested Dubravka with a curler from the corner of the box before a low ball across the face of goal from Andy Robertson just evaded Salah in the centre.
However, Alisson was required to deny Newcastle from pulling one back again when he saved at the feet of Callum Wilson after the visitors had conceded possession in midfield.
Jota headed down and wide from a Robertson cross as the game edged towards its conclusion, before the forward saw an effort cleared off the line in stoppage time after rounding Dubravka.
Nevertheless, Liverpool had done enough to record a double over Newcastle and end their unbeaten streak at St. James’ Park.