Rookie Spencer, on loan from Huddersfield, eased the Shrimps' relegation fears with a superb strike to topple the high-flying Millers.
And he feels the result has given Sammy McIlroy's side a massive boost as they bid to end a disappointing campaign on a high note.
Spencer, 19, told the club's official website: "I was really pleased when it went in, especially as it was with my weaker foot.
"We needed the points to move away from the bottom and calm the nerves, and I think you could see how much it meant to us at the end of the game.
"It was one of the best goals I've ever scored and certainly one of the most important ones."
Source: PA
Source: PA