Raheem Sterling's clinically taken opener in the eighth minute suggested a romp in line with City's 6-1 thumping of Huddersfield Town in their previous home game.
But Pep Guardiola's side switched off defensively and DeAndre Yedlin was rewarded for a lung-bursting run when Salomon Rondon picked him out to level with half an hour played.
It fell to England right-back Walker, who failed to find the net as City racked up points and goals records last season, to step forward with a long-range stunner and ensure the 10th anniversary of Sheikh Mansour's takeover was celebrated with a victory.
Newcastle undermined their bid to stifle City during the opening stages by carelessly coughing up possession in dangerous areas.
Riyad Mahrez was unable to punish Rondon's slackness but, when returning Magpies captain Jamaal Lascelles passed straight to Benjamin Mendy, the full-back found Sterling to cut inside for an emphatic finish.
Gabriel Jesus passed up two clear chances to increase City's advantage and there was an air of complacency when their disorganised backline allowed Rondon to slide a fine cross into the path of the rampaging Yedlin to equalise.
The game resumed its pattern early in the second half until a darting dribble from Sterling created the opening for Walker to crash home his rasping 30 yarder eight minutes before the hour.
Both goalkeepers excelled in the 65th minute as City's Ederson picked out substitute Bernardo Silva with a clever underarm throw.
Bernardo Silva sent a delightful pass to Sergio Aguero and his cross saw Martin Dubravka make a remarkable point-blank saves from Fernandinho before twice denying David Silva on the rebound.
Dubravka impressed again in stoppage time, driving Aguero wide to deny City's all-time top score his 15th Premier League goal against Newcastle.
What it means: City stay in touch with pacesetters
These are very early days in City's title defence but falling four points behind Liverpool and Chelsea after four games was a mildly alarming prospect Guardiola's team were able to avert, following the 1-1 draw at Wolves last time out. Newcastle lie third bottom with a solitary point but encounters with Tottenham and Chelsea have also featured in a brutal opening
Pat on the back: Salomon on song
Venezuela international Rondon was handed a thankless task as Newcastle's attacking spearhead but went about his work with gusto. The physical battle with John Stones and Aymeric Laporte was one to relish and some wonderfully astute play created Yedlin's goal. He deserves a couple of easier and more rewarding outings against opponents that will draw more ambition out of Rafael Benitez.
Boot up the backside: Jesus passes over more chances
Like Sterling, Jesus endured a goal-less World Cup. Unlike his City team-mate the Brazil striker has not picked up the baton at club level so effortlessly. His tame finish after a clever turn inside two challenges and a misjudged free header during the first-half spoke of low confidence levels.
Key Opta Facts
1,623 - DeAndre Yedlin is the first American to score in a English Premier League match since Geoff Cameron on March 23, 2014 - a span of 1,623 days. Prolonged. pic.twitter.com/KUclyjfAci— OptaJack (@OptaJack) September 1, 2018
- Manchester City have won each of their last 10 Premier League home games against Newcastle, their joint-longest run of home wins against a single opponent in the top-flight (also 10 v Wolves between 1900 and 1937).
- Newcastle have registered just one win in their last 10 away Premier League games (D3 L6).
- Since the start of last season, only Mohamed Salah (45) and Harry Kane (35) have had a hand in more Premier League goals than Manchester City winger Raheem Sterling (31 - 20 goals, 11 assists)
- Excluding own goals, Newcastle full-back DeAndre Yedlin is the first American player to score in the Premier League since Geoff Cameron for Stoke City vs Aston Villa in March 2014.
- Kyle Walker scored his first goal for Man City in all competitions in his 52nd appearance for the club.
After the international break, City are back on home turf against Fulham, while Newcastle host Arsenal.