But City still had striker Sergio Aguero to call upon and the Argentina international terrorized the Magpies all by himself.
Aguero netted a hat-trick in eight minutes and added two more strikes, becoming only the fifth player to bag five goals in a Premier League outing. Out went Newcastle's 1-0 lead, City prevailing 6-1 to take over top spot in the division ahead of city rival Manchester United.
Chelsea, though, continued to post baffling results, losing 3-1 at home to Southampton in the late kickoff -- after leading.
Aguero made it 1-1 in the 42nd minute at the Etihad Stadium with a header, got on the scoresheet again in the 49th thanks to a deflected effort and capped his three-goal burst by chipping Tim Krul in the 50th.
He completed his day of work by scoring in the 60th and 62nd minutes to emulate Robert Lewandowski's five goals for Bayern Munich in the Bundesliga against Wolfsburg in late September. Aguero was substituted shortly after his fifth.
"I'm very happy for Kun because from the beginning of the season he has in every game some chances that he normally never misses but ... he was missing some important options in the other games," City manager Manuel Pellegrini told Sky, referring to Aguero by his nickname. "Today he made a complete game playing, moving, running and scoring goals."
Kevin De Bruyne's looping volley in the 53rd minute accounted for City's other goal.
While Aguero deservedly won the plaudits, Joe Hart's contribution shouldn't be forgotten. Back from injury to replace Willy Caballero -- at fault for at least one goal in City's 4-1 defeat to Tottenham last week -- Hart made a key save to deny Aleksandar Mitrovic after the Serbian opened the scoring in the 18th minute.
Newcastle had a goal disallowed in the first half, too, prior to Aguero's heroics.
"The goal just before halftime kind of woke them up," Newcastle manager Steve McClaren told Sky. "This is the best team in the Premier League. They have a front four that can score at any opportunity.
"I've watched games here, seen other games, and every week they can score six or seven goals. What they've done is taken advantage of our missed chances."
United can reclaim first place from City on Sunday if it beats Arsenal in London.
Chelsea, the defending champion, appeared to be on its way when Willian scored in the 10th minute. But clearly suffering from a lack of confidence, Southampton pounced on Jose Mourinho's Blues.
Steven Davis converted Graziano Pelle's knock down in the 43rd minute and a combination of errors from central defenders Gary Cahill and John Terry -- who returned to the lineup -- allowed Sadio Mane to sprint through on goal and beat Asmir Begovic in the 60th.
Pelle completed Chelsea's misery in the 72nd minute, leaving Mourinho's team with a paltry eight points from eight matches and 10 points adrift of Manchester City.
Mourinho lamented Chelsea not receiving a penalty when it was 1-1 but Southampton might have had two in the opening half.
Under pressure, Mourinho vowed not to walk away and guaranteed a top-four finish for Chelsea.
"If the club wants to sack me they have to sack me, because I don't run away from my responsibilities," Mourinho, fired in his first stint at Chelsea, told Sky. "It is a crucial moment in the history of this club because if they sack me they sack the best manager this club has ever had.
"The message is that the results are the fault of the manager.
"This is a moment for everybody to assume their responsibilities and stick together."
Elsewhere, Yohan Cabaye scored and set up Crystal Palace's other goal in the Eagles' 2-0 win against West Bromwich Albion in London that sent Palace to third. Entertaining Leicester recovered from last week's 5-2 defeat to Arsenal by edging Norwich City 2-1 away, rising to fourth.
Sunderland moved off the bottom on goal difference -- northeast rival Newcastle now occupies 20th -- following a 2-2 draw at home against West Ham. It could have been better, though, for Sunderland, which led 2-0.
All eyes will now be on manager Dick Advocaat to see if the Dutchman resigns as manager, as was suggested by various reports before
Aston Villa's slide continued, a 1-0 loser at home to Stoke, while Bournemouth and Watford finished at 1-1 in a battle of newly promoted sides. Watford's Heurelho Gomes saved a penalty in the dying minutes but his counterpart, Artur Boruc, was at fault for the Hornets' goal in the first half on the south coast when he gifted the ball to opposition striker Odion Ighalo.