The Wythenshawe-born forward's sixth career goal in the fixture was arguably his best yet in a United shirt, as he struck the ball past Ederson from 25 yards, after great hold-up play by Bruno Fernandes.
Unfortunately, it was not enough to give United derby joy, as City came roaring back in the second half to win 3-1, courtesy of Phil Foden's double and a late Erling Haaland strike.
But Marcus was a worthy recipient of the league's monthly goal prize, claiming it for the first time in his eight-year senior Reds tenure.
It's the 10th time a Red has come out on top since the prize was introduced in 2016, and Rashford is the eighth different player from United to win.