The visitors started the game four points adrift of the PL summit following Arsenal’s North London derby win earlier in the day.
The reigning champions offered an early threat at the City Ground, with Kevin De Bruyne forcing Matz Sels into action shortly before Jeremy Doku sent the ball whistling past his compatriot’s post.
In response, Neco Williams stung the palms of Ederson to offer signs of encouragement to the Forest faithful.
Unfortunately for the hosts, their early hard work was undone by a simple set-piece routine just after the half-hour mark.
De Bruyne's whipped corner found the near-post run of Josko Gvardiol, who produced a glancing header to net his second league goal.
As the first half neared its conclusion, the hosts went agonisingly close to levelling from their own set-piece situation as Murillo lifted the ball over the bar after Ederson failed to punch clear from a corner.
That proved to be Ederson’s final involvement, with injury forcing Guardiola to summon Stefan Ortega at the half-time interval.
Ortega and his Man City teammates were then forced to ride a wave of Forest pressure, which saw Gvardiol make a crucial block to prevent Chris Wood from adding to his 12-goal league tally.
With Forest offering a real threat, Guardiola opted to introduce Erling Haaland from the bench in a bid to find a crucial second goal.
Fully aware of his task, the Norwegian delivered within nine minutes of his arrival, shifting the ball onto his right foot before slotting into the bottom corner to spark scenes of jubilation behind Sels’ goal.
Haaland’s 21st strike of the PL season ultimately wrapped up Man City’s first top-flight league double over Forest since 1990/91, leaving the hosts hovering just one point above the drop zone.
Flashscore Man of the Match: Kevin De Bruyne (Manchester City)