The Wales striker may have struggled against England's Three Lions last weekend, but he shot down the Tigers with a superb first-half finish.
Morison's 16th goal of the season saw Millwall leapfrog the hosts in the table to keep the Londoners in touch with the top six and still dreaming of back-to-back promotions.
City are just a point behind them but games are running out and they need to turn around the home form which sees them without a win on their own turf since February 12.
The goal came after 33 minutes when Liam Trotter won possession from James Harper in midfield and played a clever pass through to Morison, who expertly dinked the ball over City keeper Brad Guzan and into the net.
Former Lions loanee Jay Simpson came clsoe to levelling but he put an injury-time shot wide.
Source: PA
Source: PA