Mastrolía began his career with San Lorenzo.[1][2] He made his debut for the club in a Copa Argentina victory over Villa Dálmine in November 2011.[1] Mastrolía remained with San Lorenzo for three further years but never appeared in the league; though was an unused substitute twenty-seven times.[1] July 2014 saw Mastrolía join Comunicaciones of Primera B Metropolitana, whom he would make ten appearances for during the 2014 season.[1] On 1 January 2015, Mastrolía completed a move to fellow third tier outfit Platense.[1] His first appearance arrived on 17 February against Almirante Brown, the first of twenty-seven in his opening campaign.[1]