The Spartans upset the 11th-ranked Bulldogs in the Virginia 5A North region quarterfinals. (Abigail Fazio for Synthesis/Koubaroulis LLC./The Washington Post)

Quarterback Brady Reitzel scored the winning touchdown with 45 seconds left to lift Broad Run to a 23-21 win against No. 11 Stone Bridge in a Virginia 5A North quarterfinal between the two Ashburn rivals.

The win was the first for the Spartans (9-3) in the head-to-head series against the Bulldogs (9-3).

“This is a big win for us. It’s a playoff win,” Spartans Coach Matt Griffis said. “These two teams have a great tradition.”

Broad Run led 17-7 early before Stone Bridge edged back ahead 21-17 with less than six minutes to play.

“I just told the kids that we’re fine and that we are destined to win this ball game,” Griffis said. “And I think the kids had it in their minds they were going to refuse to lose.”

The hero of Friday night’s upset at Stone Bridge, Brady Reitzel gets another crack at No. 4 Briar Woods in next week’s Virginia 5A North region semifinal. (John McDonnell/The Washington Post)

The Spartans will face the third Ashburn school, No. 4 Briar Woods (11-1), in a Virginia 5A North semifinal next week.

The Falcons beat Mountain View, 49-7, in a region quarterfinal on Friday behind five touchdown passes from quarterback Trace McSorley.