Potomac School beat Flint Hill, 9-7, in 10 innings in the Independent School League softball championship. (Kyle McFadden/Washington Post)

Correction: An earlier version of this story misidentified the Flint Hill player who hit an RBI double to tie the score at 4-4 in the seventh inning.

With a towering blast, Potomac School’s Charlotte Thompson turned innings of anxiousness into inevitable jubilation.

Picking up a team that had let a three-run lead slip away in Tuesday’s Independent School League softball championship, Thompson belted an emphatic grand slam in the top of the 10th inning, sending Potomac School to a 9-7 win against Flint Hill.

“We didn’t give up,” said Potomac School Coach Wayne Loving, whose team led 3-0 in the fourth inning but allowed the Huskies to claw back. “We stayed in there. It means a lot to win this. We battle them down to the wire every time.”

Tuesday provided a dramatic chapter to what Potomac pitcher Maria Urban called a “deep-seated rivalry.” Last year, the Panthers beat the Huskies in the bottom of the seventh inning to win the ISL title. On April 11, Flint Hill handed Potomac its first loss of the season in a one-run contest.

This time, on a sunny day in Alexandria, Potomac felt more prepared, fresh off a 9-3 defeat to O’Connell on Friday in the Virginia Independent Schools Athletic Association championship. This ISL title game was being played after the VISAA one because of multiple postponements.

After a breezy first two innings, Potomac powered ahead with two runs in the third and another in the fourth to lead 3-0.

While the Panthers’ offense took control, Urban, a sophomore, struck out nine Huskies in the first four innings. But Flint Hill’s offense eventually found a way to get to her. The Huskies got on the board with a two-out single in the fifth, Grace Hausamann scored on a wild pitch in the sixth, and then Amber Carrico’s sacrifice fly made it 4-3 later that inning.

Flint Hill pitcher Natalie Plaut sent the Panthers down in order in the top of the seventh, and then Tess Brady’s two-out double down the right field line tied it at 4-4.

“It can get discouraging sometimes, but you have to fight,” said Urban, who finished with 15 strikeouts and 140 pitches.

Potomac center fielder Yanna Bravewolf prevented further damage with three run-saving catches as the teams battled into extra innings.

After Potomac finally scored again in the 10th, Thompson made the lead a bit more comfortable with her grand slam.

“When that left my bat,” Thompson said, “I had no doubt.”