Mathis immediately took his game to a new level, flashing an "I ♥ NY" shirt after scoring goals and breaking the MLS record by scoring five goals in a game against Dallas Burn on August 26, 2000. He finished second in the league in scoring with 16 goals and 14 assists and was named to the MLS Best XI. 2001 saw Mathis score seven goals in his first six games, including the league's eventual Goal of the Year on a half-field run against Dallas. In June, he tore his ACL, which ended his season. He never recovered his pre-injury form and scored only 13 goals in his remaining two seasons with the MetroStars.