Hawkins was handed the gloves by Becky Langley in her first match since becoming a full-time footballer and certainly didn't disappoint, making some big saves in the initial 90 minutes before proving to be the difference in the shoot-out thanks to her save from Mascarello.
The Magpies found themselves 2-1 down after 87 minutes and heading for their first defeat at St. James' Park, before Amy Andrews' delicate late finish sent the match to penalties.
And Hawkins admitted one key moment aided her just before she dived to her right to repel Mascarello's spot kick at the Gallowgate End.
"I love penalty shoot-outs because it's just you against one other person," Hawkins told newcastleunited.com.
"It's about who's got the most bottle. I looked at her and she kind of stared at that side, then started at me so I thought, you're trying to make me go the other way.
"I knew I just had to throw myself at it. Then, once I've saved one, we’ve got the upper hand in the penalty shoot-out. It's a win-win for us (goalkeepers)."
Hawkins started the final two games of last season for United, recording successive clean sheets as Langley's side rounded off another successful campaign.
The Scottish shot-stopper was only part-time last season but now, with the club's full backing and support aiding their transition into their full-time model, Hawkins knows she’s living out a dream.
"This is what you start playing football for as a kid, to be in these sorts of situations," she said. "It was unbelievable and just a dream come true.
"I'm feeling great and have been supported massively by the club, transitioning from a full-time job last season to becoming a full-time footballer.
"Personally, I know this is going to help me massively as a player and a person."
Despite falling behind midway through the first half on Saturday, United pulled off an impressive comeback against European opposition.
Hawkins acknowledges that there are plenty of positives to take from the club's second pre-season outing, including the role of people behind the scenes.
"It was only our second game of pre-season so it shows the resilience that we've got," she added.
"To concede two goals against a team like AC Milan, some sides may have crumbled, but we stuck to our game plan and executed it.
"The players that came on, you'd not have noticed any different but for their fresh legs and giving us that extra bit of energy to get a goal.
"It's a massive credit to not just the ones who are playing, but all of the team and backroom staff."