The 28-year-old settled Wednesday's shootout 5-4 after Bruno Fernandes missed United's earlier attempt and Leeds United's James Justin struck the crossbar, sealing victory following a 1-1 draw in front of a rare capacity crowd at the home of Gaelic games.
"It's nice to score the winning penalty, but even in friendlies, the aim is to win the game," Mazraoui told MUTV. "I think the best way to prepare for the full season is to go into every game to win. Even here, you can feel the rivalry of this game. It was an amazing atmosphere."
Mazraoui reported back to training last week after helping Morocco reach the World Cup quarter-finals over the summer, and played the final 30 minutes at Croke Park having also featured briefly in Manchester United's earlier draw with Paris Saint-Germain. Despite the limited minutes, he said he feels close to full fitness.
"I don't think you lose too much in three weeks off. I've played a lot of games at the World Cup, so physically, I'm not too far off from being at my top level. I feel fresh and I'm ready to begin the new season."
The former Bayern Munich and Ajax defender also credited United's existing squad with helping this summer's new arrivals settle quickly, singling out midfielders Andrey Santos and Youri Tielemans.
"They've settled in really well. We have a good group of guys - very easy going, and I think we have players who give this feeling to the new signings," he said. "You can see that straight away in the quality they show in games."
Mazraoui was similarly impressed by the younger players who have featured throughout pre-season, though he stopped short of naming individuals.
"Amazing - they did really good. I gave them a compliment in my last interview, so I'm not going to say any names, it's going to be too much! The experience they'll get from these kind of games will really help them in the future, and I hope it gives them more hunger to show that they belong here."
United's final pre-season fixture takes them to Wroclaw, Poland, on 15 August to face Ruben Amorim's AC Milan, a reunion Mazraoui is looking forward to after playing under the Portuguese coach at Old Trafford.
"It's a big game against a big team. Of course, we all know Ruben, so it'll be good to see each other again."