Doku ended Brentford's stubborn resistance on the hour mark at the Etihad Stadium when he curled a fine finish in the top corner.
It was the Belgium winger's fourth goal in his last three games in all competitions for City, including a pair of dazzling efforts in a 3-3 draw at Everton on Monday.
City's failure to beat Everton has taken the destiny of the title race out of their hands, but Doku ensured they kept the pressure on leaders Arsenal.
Pep Guardiola's men are two points behind the Gunners, who travel to struggling West Ham on Sunday.
"Jeremy is outstanding in many things. Looks like a final product already and of course he can improve," Guardiola said.
"Always had this incredible ability to dribble and to make action and connection, it's outstanding.
"But now it's winning games. I'm so incredibly pleased to have a guy that brings energy and that can score goals."
Arsenal will clinch the title if they win their last three games against West Ham, Burnley and Crystal Palace.
"We will see, that is not in our hands. We will do our job. We didn't do it perfectly with Everton. We will do our job and wait," Guardiola said.
"We suffered in the first minutes today but after that we played a really good game. Especially left side in the first half, both sides in the second."
Guardiola conceded City's failure to close out games at times this season is likely to prove their undoing.
"Everton was the real proof, 3-1 down and emotions. The second half we give away. It happened last season many times, now we're more solid but we still give away," he said.
"That's football, it's how you react. I'm pleased for the way we have done it."