His header, off a free kick from Harrison Shipp in the 60th minute broke a 1-1 tie between the two Atlantic Coast Conference teams.
Afterward, Notre Dame coach Bobby Clark had a little bit of fun at O'Malley's expense.
"He missed a few all season, I can tell you, but he saved that goal for the right time," said Clark, laughing. "It was a great goal."
O'Malley, whose primary duty is stopping goals but who scored three this season, said that earning the goal in a familiar venue was an additional bonus.
"It is extra special doing it so close to home," he said.
Last year's homecoming was bittersweet.
O'Malley suffered a sprained knee ligament during Notre Dame's Big East championship win over Georgetown, which was also played at PPL Park.
The injury forced him to miss last year's NCAA tournament, when top seeded Notre Dame lost to eventual national champion Indiana, 2-1, in double overtime in the round of 16.
"Obviously getting hurt in the final and not being able to play in our loss to Indiana was heartbreaking," O'Malley said. "It is good to get a little bit of a cathartic victory there."
O'Malley is truly a study in perseverance. He didn't play at all as a freshman and played just one game as a sophomore before becoming a starter last season.
"It was the first time in his life he had to sit on the bench and we were going to see what kind of character he was made of," said his father, Thomas O'Malley, in a telephone interview after the game. "It was extremely difficult for him but he channeled it and said he was going to dedicate himself to becoming a two-footed player."
Now O'Malley is dangerous with either foot, not to mention his head.
His father, who is the executive director of FC Delco, among the top soccer clubs in the country, said he was thrilled for his son but felt for Maryland keeper Zack Steffen, a Downingtown West graduate and an FC Delco alum.
"You are torn having one FC Delco player against another because Zack is a great goalie and person," Thomas O'Malley said. "But it was a thrill to see him score such a big goal."
It's a goal that Andrew O'Malley will no doubt have to recount numerous times throughout the rest of his life, an exercise that will likely never get old.