His two close-range goals secured Palace’s third straight away league victory, as they bested United 2-0 on Sunday.
Mateta, who has now scored six goals in five league games this year, said he feels fantastic and full of confidence.
Mateta stated post-game: “I'm feeling fantastic, I'm feeling very good!
“We won these three points. We lost and we gave (away) three points last week, and we work hard for the three points (today), so I'm very happy.
“We know how they (Manchester United) play, with their new manager. We worked on the video in the week, and we stuck to the plan.
“Today we just stuck to the plan, listened to the gaffer and worked hard, and I think we deserved this win.
“I just put my head down and kept working hard. I think, when you work hard, sometimes you deserve the rewards.”