Watson, of Boys' Latin Charter, became just the fourth player in the Pub's 112-year history to eclipse 2,000 career points.
He looked up and pointed to his girlfriend in the stands - she was the first person he saw, he said - acknowledging later that he had to hold back tears.
His teammates and classmates rushed the court at Shepard Recreation Center at 57th Street and Haverford Avenue. Play stopped for a little less than two minutes as photographers and camera people huddled around the 5-foot-10, 160-pound guard. He hugged teammate Yahmir Greenlee like a brother.
Watson finished the game with 22 points to lead all scorers, as Boys' Latin beat Gratz, 80-59. He shot 9 for 17 from the field with four rebounds, seven assists, and six steals.
Above all, he joined a list of elite Pub greats: all-time leading scorer Maureece Rice (Strawberry Mansion), Wilt Chamberlain (Overbrook) and Tyrone Garland (Bartram), a former AAU teammate of Watson's.
"I'm grateful that I can be mentioned in the same breath as Wilt Chamberlain," Watson said. "And it's even better that I can do it in the gym right across the street from his house, basically."
Chamberlain eclipsed 2,000 points in the 1950s, graduating in '55.
Watson, committed to Boston University, reached 1,000 points on Feb. 17, 2010, as a sophomore. As a junior, he scored a career-high 43 points. As Thursday took its course, Watson said his stomach was "in knots." It was the most nervous he's ever felt, he said.
On the first Boys' Latin possession, Watson floated an alley-oop pass to teammate Carlos Taylor, to a loud ovation by the crowd.
The Warriors (14-4 overall, 7-3 league) smothered Gratz (2-10, 1-8) with half-court traps and full-court presses, and Watson dominated the tempo.
His team went into halftime leading by 19. A 9-0 run to start the third quarter, in which Watson assisted two buckets and scored another, put the Warriors ahead by 28.
Perhaps no one in attendance was prouder than Watson's father and head coach, Maurice Sr., the only basketball mentor his son has known.