The England international joined United earlier this month from Chelsea for 55 million pounds ($71.45 million), according to British media reports.
"When we turned up last night and when we turned up at the stadium today, the support has been amazing. They came out and showed up for us today and it's amazing to see," he told MUTV after playing the first 45 minutes of the match.
"This is what we want to play for and we want to make them proud."
Manager Erik ten Hag praised the club's first close-season signing, with the Dutch manager looking to strengthen his squad ahead of United's return to the Champions League.
"Oh (he was) great, but we could expect this. He has so many skills and I'm sure we will take so much joy from him. He will contribute to our performance, absolutely," he said, adding that there was more to come from Mount on the pitch.
United kick off their Premier League campaign on August 14th at home against Wolverhampton Wanderers.
See a summary of United's friendly win against Leeds at Flashscore
