Jean-Philippe Mateta’s two goals secured their fifth away victory in six league matches.
Palace also kept a fourth straight clean sheet on the road, extending their club-record unbeaten run to eight games.
Post-game, Richards was effusive in his praise of the team, stating: “If I’m self-critical I remember a few (mistakes), but it felt like we had a pretty solid game, and I think it's probably our best game collectively this season!
“United are always going to be a quality team, so there was a bit of back and forth throughout the game, especially the first few minutes in the second-half, but we just kept patient and we knew that we would get our chances and hopefully score from them.
“It's always good to get a win, especially in an away fixture, so we're very happy all around today.”