McNew ended the suspense quickly, getting a pin in just 29 seconds.
Unionville had jumped out to a 12-3 lead off consecutive pins, by Nate Chaclas at 120 pounds and Ian Larson at 126.
The Indians expanded their lead to 24 points, 27-3, with seven matches remaining behind three decisions - by Mike Caldwell at 132, Joey DiMarco at 138, and Tyler Crossman at 152 - and a pin from Zach Pfeifer at 145.
The teams then swapped pins - Steven Phillips winning for the Bucs at 160, and Connor Reilly answering for Unionville at 170 - to make the score 33-9.
But Interboro stormed back. Keith Thomas pinned at 182, Sonny Armstrong triumphed by forfeit at 195, and Eric Owens (220) and heavyweight Matt Gould posted falls to create a 33-33 tie.
McNew then won the 106-pound bout and the championship.
"They're just solid," Interboro assistant coach Dan Meli said of the Indians. "They were tough top to bottom, and they wrestle physically strong and mentally strong."
UNIONVILLE 39, INTERBORO 33
113: Jay Bryan, I, dec. Bobby Murray, 6-5; 120: Nate Chaclas, U, pin Mike Wasch, 5:23; 126: Ian Larson, U, pin Noel Cruz, 0:44; 132: Mike Caldwell, U, dec. Joey Gonzales, 7-6; 138: Joey DiMarco, U, dec. Jeff Finley, 4-0; 145: Zach Pfeifer, U, pin Paul Bilardo, 4:08; 152: Tyler Crossman, U, dec. Cody Mathis, 8-1; 160: Steven Phillips, I, pin Jamie McNew, 0:41; 170: Conner Reilly, U, pin Joe Koke, 0:51; 182: Keith Thomas, I, pin Ryan Margolin, 4:45; 195: Sonny Armstrong, I, won by forfeit; 220: Eric Owens, I, pin Evan James, 0:32; 285: Matt Gould, I, pin Will Hart, 0:42; 106: Will McNew, U, pin Shane Mathis, 0:29.
Contact Austin Odenbrett at firstname.lastname@example.org.