Johnson's father, Mike, was part of Chester's 1989 state-championship squad. Now deceased, he played at Coppin State with current Clippers coach Larry Yarbray.
Against Rustin, Mahir Johnson registered 20 points, including a trio of three-pointers, before intermission. The Clippers took a 36-20 lead into the locker room.
"We didn't know too much about Rustin coming in," Johnson said. "We were more concerned with playing our game and doing our normal things."
Overall, Johnson shot 7 for 13 from the field (4 for 4 from beyond the arc) and 11 for 12 from the line. He added six rebounds and two steals.
"He's solid," Rustin coach Keith Cochrane said. "You can't leave him open. Once he gets his feet set, it's going in."
Chester, moving closer to its 23d district title, will face fifth-seeded Pennsbury for the championship at 9 p.m. Friday at Villanova's Pavilion. In last year's final, Chester downed Lower Merion, 60-46.
The Clippers (21-5) practically lived at the foul line against the Golden Knights, converting 29 of 36 attempts. They were 23 for 28 from the line in the second half.
Sturdivant, who has committed to Stony Brook, produced 21 points, 10 rebounds, and 3 blocked shots. Senior guard Conrad Chambers recorded seven second-half points and five assists.
Junior Andrew Chobany paced West Chester Rustin (17-9) with 26 points and 10 boards. He netted 14 points, including four treys, in the third quarter.
The Golden Knights shot 16 for 61 (26.2 percent) from the field (5 for 30 in the first half). They were 6 for 29 (20.7 percent) from three-point range.
West Chester Rustin 8 12 19 17 – 56
Chester 16 20 21 15 – 72
WCR: Ethan Ridgeway 8, Andrew Chobany 26, Matt McCarrick 3, Brennan Halverson 9, Tyler Blake 6, Justin Ammerman 2, Dane Anderson 2.
C: Khaleeq Campbell 8, Conrad Chambers 7, Keyonte Watkins 4, Tyrell Sturdivant 21, Mahir Johnson 29, Marquis Collins 3.