The England forward was voted PFA Player of the Season in 2023-24 when he scored 27 times in all competitions for City, including a double on the final day of the season against West Ham to clinch a fourth successive title.
But Foden's form vanished last season and the goals dried up, and before Sunday, his last Premier League goal was in January.
His struggles were one factor in City's troubling campaign last season, but there were signs on Sunday that he is emerging from his slump and that the joy that manager Pep Guardiola said had gone from his game is returning.
"We missed him so much last season. We need him so much," Guardiola told reporters after City avoided a third successive defeat in the Premier League.
"When he moves behind the strikers, in that position, the sense of goal, the sense of turns, the quality to keep the ball... There are players that play behind the striker, and most of them pass the ball and stay and (say) 'look how good I make the pass'. He's a guy who makes a pass to the penalty spot like an animal. When he doesn't get the pass (back) he's angry, because he wants to score."
"We can't forget two seasons ago he was the most important player in the Premier League and was the key player in that title. Last season, for various reason,s he could not be with us."
Foden offered a glimpse of his old self when he scored twice in the FIFA Club World Cup at the end of the last campaign, but injury niggles meant his only appearance since the start of the season was a brief cameo off the bench in City's home defeat against Tottenham.
Given a start on Sunday, Foden needed only 18 minutes to end his Premier League goal drought, heading in Jeremy Doku's cut back for his seventh goal in Manchester derbies.
"Hopefully, step by step, he can get back to his best," Guardiola added. "(With) the joy and happiness we see in his face every day lately, now we are sure that we are going to see the best Phil."
Haaland's brace, taking his Premier League tally to five in four games, added to the five goals he scored for Norway in midweek against Moldova.
"Erling never disappoints us since he arrived," Guardiola said. "Erling has the commitment, that is why he signed a contract for many years. He's a special player."