The talismanic skipper had netted his sixth of the campaign to seal three points at Burnley in the black and whites' last outing; his seventh came in the 71st minute of a hitherto nervy game at St. James' Park, before, from a Guimarães corner, Malick Thiaw added a second to make it back-to-back wins for the Magpies.
The visitors had frustrated United for large spells of the game before their captain led by example once more - soon after head coach Howe had made a bold triple substitution which ultimately altered the course of the match.
On a cold afternoon on Tyneside, Yoane Wissa, making his second successive start after scoring at Turf Moor on his full Premier League bow for the club, had an opportunity after three minutes. Anthony Gordon raced onto Joelinton's pass and cut the ball back towards the penalty spot, but Dean Henderson held Wissa's low left-footed shot.
Will Hughes saw a shot deflected over for Palace and Fabian Schär - on his 250th appearance for the club - had a header kept out by Henderson before, in the 19th minute, United thought they had taken the lead.
Guimarães played a delightful ball for Wissa, who unselfishly squared for Gordon to convert, but VAR intervened, with Wissa narrowly offside.
Referee John Brooks waved away appeals for a Newcastle penalty when Thiaw was hauled to the ground by Hughes as Lewis Miley swung in a corner, then Lewis Hall tested Henderson with a long-range left-footed effort.
United had the ball in the net for a second time when Joelinton slotted home after controlling Schär's raking pass, but the flag was up against the Brazilian.
Jean-Philippe Mateta and Hughes both came close for Palace just before half time, then Nick Pope denied Eagles debutant Brennan Johnson midway through the second period.
Howe introduced Jacob Ramsey, Harvey Barnes and Tino Livramento in the 64th minute as the Magpies searched for a breakthrough.
That finally came when - after a Guimarães corner had hit the bar as the United skipper looked to replicate his Olimpico goal against Burnley - the skipper came back for more moments later.
Barnes swung the ball in after Jacob Murphy's free-kick was half cleared, Miley forced the ball back across goal and Guimarãres was there to apply the finishing touch with his head.
Henderson made a great save from a Barnes header soon afterwards, but from the resulting corner, Thiaw prodded home to double Newcastle's advantage in the 78th minute.
It could - and probably should - have been 3-0 when, in stoppage time, Barnes sprinted onto a Miley pass to go through on goal. Henderson blocked with an outstretched leg but Willock was following up, only to fire wide. But United started 2026 just as they ended 2025: with three Premier League points.
Newcastle United: Nick Pope, Lewis Hall (Tino Livramento 64), Fabian Schär, Joelinton, Sandro Tonali (Jacob Ramsey 64), Yoane Wissa (Nick Woltemade 78), Anthony Gordon (Harvey Barnes 64), Malick Thiaw, Jacob Murphy (Joe Willock 88), Bruno Guimarães (c), Lewis Miley
Substitutes: Aaron Ramsdale, Kieran Trippier, Sven Botman, Alex Murphy
