The 18-year-old hit a magnificent hat-trick and produced an assured all-round display as we moved through to the quarter-finals of the competition for the seventh-consecutive season.
Park was exceptional throughout, with her third goal a magnificent 30-yard strike that left Nikita Runnacles with no chance.
And Mahon was quick to praise his young forward, lauding her composure in front of goal.
“The girls took their chances second half,” he said.
“For the likes of Jess Park to step up and play like that and be as composed as she was, I was really proud.
“Jess is a top player. This is the start of her career and she’s doing exceptionally well.
“It was a good day for her today.”
TICKETS: City v Chelsea Women | Sun 23 Feb
City are now safely into the last-eight draw, which takes place on Monday evening at 8.45pm.
We are looking to win the competition for the third time in four seasons, with our most recent success coming back in May as we beat West Ham 3-0 in the final.
And Mahon says the motivation to retain the trophy is high among the squad.
"It’s an iconic trophy and we want to win it, it’s ours," he said.
"Whoever we get we will prep right for. I've said a lot I only focus on the next game. We’re already prepping for Chelsea.
"Whatever happens with the draw, we will be prepared when it comes around."