The Terps battled back from a deficit at halftime, knocking off the Cavaliers at Audi Field.
Goals from Joshua Bolma and Chris Rindov kept the Terps' perfect record in tact.
Two goalkeepers are battling for a spot in the starting 11.
The Terps beat then-No. 18 Charlotte and UMBC to climb the rankings.
The freshman forward scored in his first game as a Terp and impressed players and coaches throughout opening weekend.
The Terps scored three first-half goals and held off a late charge from the Retrievers to remain undefeated.
Freshman Caden Stafford scored the lone goal of the match, opening his Terp career on a high note.
The Terps open their season against No. 18 Charlotte on Thursday.
Vaughn's contract came into effect July 2020 and will run through June 2026, securing the head coach that brought the Terps to the NCAA tournament for the first time since 2017.
Cowles was the second and final Maryland player taken in the draft.