Johnson scored the winner shortly after being introduced from the bench
By Phil Dawkes
Manchester City were not at their best but secured a hard-fought win over a spirited Newcastle to move second in the Premier League.
City took the lead through a Carlos Tevez penalty after Mike Williamson was deemed to have fouled the Argentine.
But Newcastle, who lost Hatem Ben Arfa to a suspected broken leg, levelled via a close-range Jonas Gutierrez drive.
Substitute Adam Johnson won the game for City shortly after his introduction with a superb low drive.
Despite still being four points behind
Chelsea, who beat Arsenal in the day's late kick-off,
the victory did move City second in the table - a sign that a spending spree that led to the club announcing a 12-month £121m loss on Friday might be beginning to show a return.
In their previous league match, City produced an impressive display to beat Chelsea 1-0 but they were unable to reach such heights against a disciplined Newcastle side, who will feel their efforts deserved greater reward.
Kidd pleased after 'ugly' win
But City's money has given them a talented squad that can start with the likes of eventual match-winner Johnson on the bench, which is a luxury Newcastle cannot afford.
This was demonstrated early on when the visitors lost Ben Arfa - who has impressed since joining on loan from Marseille following a strong challenge from Nigel De Jong.
They would also lose centre-back Fabricio Coloccini to a groin injury before half-time.
When the game restarted following Ben Arfa's injury, City quickly took control and were ahead in the 17th minute when Tevez improved upon his record of having scored half his side's goals this season with a fiercely struck penalty.
The awarding of the spot-kick itself was a controversial decision by referee Martin Atkinson, who judged that Williamson had fouled Tevez in the box when it appeared he had got a toe to the ball.
But Newcastle rallied and were firstly denied an equaliser when Joe Hart tipped Coloccini's long-range drive past the post before a superb strike from Gutierrez drew them level.
Gutierrez's initial cross was blocked by Kolo Toure but the Argentine winger collected the loose ball in the box and blasted a powerful rising shot past Hart from 10 yards.
For the remainder of the half, the industrious Newcastle were the better side but the chances fell to City, with Gareth Barry wasting the best of them when he was found in space on the right but firstly delayed his cross before eventually allowing Newcastle to block his poorly directed attempt.
The visitors were similarly industrious at the beginning at the start of the second half but only had a wayward effort from Wayne Routledge to show for it.
City looked dangerous when they broke and Tim Krul was kept busy by a powerful angled drive from Tevez and a low cross from half-time substitute Emmanuel Adebayor.
In search of something fresh, Mancini introduced Johnson - who the manager recently suggested should work harder to earn a place in the starting line-up - for Barry and the change paid immediate dividend.
Hughton bemoans penalty decisions
In the 72nd minute, the England winger collected the ball on the right and weaved through two challenges before unleashing a rasping low drive that found the bottom corner of the net.
However, in keeping with their overall performance, Newcastle refused to lie down and maybe should have been given the chance to level from the spot when Ameobi appeared to be fouled by Joleon Lescott only for Atkinson to wave away the protests.
Newcastle would have one further chance to salvage something from the game, but Williamson was unable to direct his header from a corner on goal.
Manchester City assistant manager Brian Kidd: "Adam [Johnson] is always capable of producing something like that.
"The great thing was the response from players. The players weren't happy at half-time and it's great to see their hunger. The players are setting their own standards now.
"Hopefully if we can win games like this we can be in contention [for the title] at the end of season."
Newcastle boss Chris Hughton: "We set the team up to play against their quality but key decisions went against us.
"My first impression was that it [the Tevez incident] was not a penalty, and that has not changed. The touch [by Mike Willamson] on the ball was outside the penalty box, and that was confirmed when we saw the replay at half-time. It was a dreadful decision on the same side as the linesman.
"Ameobi had his standing foot taken away from him, Lescott loses his footing, and it's an absolute penalty.
"We're pushing to get an equaliser and I can't fault the attitude of the players but we need things to go for us - and those two dreadful decisions have gone against us."
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