Match ends, Newcastle United 0, Leicester City 3.
Leicester's impressive season continued with a dominant win at Newcastle - and the Foxes' potential "excites" manager Brendan Rodgers.
Victory keeps the East Midlands club second and inflicts a third straight defeat on Steve Bruce's side, who played almost the whole second half with 10 men following a string of injuries.
Leicester, without the division's leading goalscorer Jamie Vardy for the second successive game, took the lead through Ayoze Perez, who kept his cool to finish well against his former side after being gifted possession by a horror pass from Florian Lejeune.
The Newcastle defender was culpable again just a few minutes later as his weak clearance was claimed by the away side and fed to James Maddison, who rifled in a thunderbolt of a second from the edge of the box.
The home side, whose best effort fell to a woefully ill-equipped and confidence-shorn Joelinton to waste, were unable to respond and would have lost by much more but for an inspired display from goalkeeper Martin Dubravka.
Dubravka was powerless to prevent substitute Hamza Choudhury scoring a superb third, curling in his first goal in senior football from the edge of the box.
It was the final blow for the home side, whose afternoon started badly and only got worse. Both Jetro Willems and Javier Manquillo were forced off through injury at the end of the first half, before Fabian Schar followed them at the start of the second, leaving them with 10 men following the half-time substitution of the also injured captain Jonjo Shelvey.
"I remember coming here before with Liverpool and we won 6-0 and played very well," said Rodgers.
"We've come here today with equally as good a performance, not scored the goals, but certainly with the control in the game and the quality in our game, played very, very well.
"But we can play better. We will improve the longer we work together - because it's only been 10 months or so.
"The potential in the group really excites me, but we have to keep that consistency and that hunger to want to be better."
Newcastle remain in mid-table but their points cushion above the relegation zone is down to five.
There are no such concerns for Leicester, though, with this win keeping them in second, ahead of Manchester City.
It was also Leicester's seventh away Premier League win of the season - only unbeaten leaders Liverpool have managed more.
Foxes begin big seven days in style
Back-to-back defeats by reigning champions Manchester City and runaway leaders Liverpool either side of Christmas dealt an almost certainly fatal blow to Leicester's title aspirations. The Foxes are actually two points better off now than at this stage of their remarkable 2015-16 title win, but the imperious form of Jurgen Klopp's side makes a repeat triumph even more improbable.
However, this victory, four days after the win at West Ham, keeps the Foxes at least notionally in the hunt, restores the sense of supreme confidence that existed prior to the trip to the Etihad and sets them up for what is a crucial seven days in their season.
On Saturday they face Wigan in the FA Cup third round, followed four days later by the home first leg of their Carabao Cup semi-final with Aston Villa.
Brendan Rodgers took the opportunity to rest a host of players for the game at London Stadium, correctly trusting in a talented second string to get the job done against a woefully poor Hammers side in the death rattle of Manuel Pellegrini's managerial reign.
He was further rewarded for this decision - and the one to switch to a back three, with Ben Chilwell and Ricardo Pereira as wing-backs - at St James' Park with a display full of energy and, once they had a cast-iron grip on the encounter, sensible game management.
Such was the efficiency of their display they did not miss Vardy, who recently welcomed the birth of a daughter. Perez was full of clever running and ruthless against his former side, while Maddison and his replacement Choudhury brought their shooting boots and then some.
Choudhury's strike, in particular, added insult to injury as it was his tackle in a meeting between the sides in August that resulted in the serious injury that keeps Matt Ritchie out to this day.
A very bad day at the office
Where to even start with Newcastle?
In defiance of some of the doom-mongering that greeted Steve Bruce's appointment as Rafael Benitez's successor in the summer, the Magpies have enjoyed a solid season so far - unspectacular but resilient.
This all came undone, though, during a 90 minutes strewn with errors and misfortune.
Joelinton has failed miserably to endear himself to the Toon Army during the first half of the season and only further blotted his copybook with two awful misses - the first the more crucial, coming with the score 0-0 and seeing him head a follow-up to his own blocked shot away from rather than towards the goal.
The second, later in the game, saw him slice a clear shot on goal following a pull-back from the byeline.
It was in defence that the wheels really came off, however, with Lejeune playing a key and calamitous role in both of Leicester's first two goals.
The injuries to his fellow defenders Willems and Manquillo gave Bruce one final role of the dice with his replacements, which he used at the break to usher Sean Longstaff into the game in place of Shelvey, who was also injured.
When Schar then pulled a thigh muscle, he limped out the game and took any hope Newcastle had of getting back into the game with him.
The ramifications will stretch beyond Wednesday, with Newcastle now having to cope with 10 injuries in a squad of 22 senior outfield players.
'All three goals were wonderful'
Leicester manager Brendan Rodgers to BBC Sport: "We played very well in the first half with a new system. The players had great fluency. We pressed really hard.
"We worked them in the second half, stretched the game and it led to the third goal. All three of our goals were wonderful. James Maddison is a magical player who has so much talent and confidence.
"We are so happy for Hamza Choudhury to get his first goal - he's a local boy who loves Leicester City.
"There is no way on this earth that you can ask players to play at the intensity we want without making a lot of changes. We made changes at West Ham and again today.
"Jamie Vardy has a tight calf, he is being treated and I didn't want to take any risks."
Leicester on the ball - match stats
- Leicester averaged 77.1% possession against Newcastle - their highest figure in a Premier League away game since the start of 2003-04.
- Leicester have won six of their past seven league games on New Year's Day (D1).
- The Foxes have lost only two of their past 13 Premier League games, winning 10 of those matches. In fact, they have won six of their past seven away league games (L1).
- After going eight consecutive home Premier League games without defeat, Newcastle have now lost back-to-back matches at St James' Park.
- Since the start of last season, Leicester's James Maddison has scored eight Premier League goals from outside the box - more than any other player.
- Only Liverpool (16) have had more different goalscorers (excluding own-goals) in the Premier League this season than Leicester City (13).
- Leicester's Ayoze Perez has been directly involved in eight goals in his past five league appearances at St James' Park (six goals, two assists).
After home cup games against Wigan and Aston Villa, Leicester's next league game is at home against Southampton on 11 January (15:00 GMT kick-off).
Newcastle travel to Rochdale in the FA Cup third round before going to Wolves for a Premier League game on the same day the Foxes host the Saints (15:00 GMT).
- 5SchärSubstituted forat 51'minutes
- 18FernándezBooked at 31mins
- 19ManquilloSubstituted forKrafthat 45+3'minutes
- 8ShelveySubstituted forS Longstaffat 45'minutes
- 15WillemsSubstituted forYedlinat 45'minutes
- 36S Longstaff
- 6EvansSubstituted forMorganat 84'minutes
- 21Ricardo Pereira
- 8TielemansBooked at 59mins
- 10MaddisonSubstituted forChoudhuryat 77'minutes
- 14IheanachoSubstituted forGrayat 63'minutes
- Martin Atkinson
- Shots on Target
Second Half ends, Newcastle United 0, Leicester City 3.
Attempt missed. Demarai Gray (Leicester City) right footed shot from outside the box is close, but misses to the left. Assisted by Youri Tielemans following a fast break.
Foul by Ayoze Pérez (Leicester City).
Federico Fernández (Newcastle United) wins a free kick in the defensive half.
Goal! Newcastle United 0, Leicester City 3. Hamza Choudhury (Leicester City) right footed shot from outside the box to the top right corner. Assisted by Wilfred Ndidi.
Demarai Gray (Leicester City) wins a free kick on the left wing.
Foul by Federico Fernández (Newcastle United).
Substitution, Leicester City. Wes Morgan replaces Jonny Evans.
Foul by Ben Chilwell (Leicester City).
Yoshinori Muto (Newcastle United) wins a free kick in the defensive half.
Substitution, Leicester City. Hamza Choudhury replaces James Maddison.
Foul by Ricardo Pereira (Leicester City).
Martin Dubravka (Newcastle United) wins a free kick in the defensive half.
Corner, Leicester City. Conceded by Miguel Almirón.
Attempt missed. Demarai Gray (Leicester City) right footed shot from the centre of the box is close, but misses to the right. Assisted by Youri Tielemans.
Offside, Leicester City. Ricardo Pereira tries a through ball, but Ayoze Pérez is caught offside.
Substitution, Leicester City. Demarai Gray replaces Kelechi Iheanacho.
Wilfred Ndidi (Leicester City) wins a free kick in the defensive half.
Foul by Joelinton (Newcastle United).