Thornton Academy’s Christopher Balzano reaches for the throw as Falmouth’s Gus Ford slides into second with a stolen base. (Shawn Patrick Ouellette/Portland Press Herald)

SACO — With two outs in the top of the seventh of a tie game, Falmouth High junior Ike Kiely knew he needed to get something going.

Did he ever. Kiely turned on an inside fastball from Thornton Academy freshman reliever Cody Bowker and drove it over the left-field fence for a solo home run.

“I didn’t know it was gone until I rounded second base and heard my teammates screaming. Wow. What a feeling,” Kiely said.

Kiely’s blast was backed by clutch relief pitching from freshman Dom Tracy to finish off a 5-4 upset of No. 2 Thornton Academy (14-3).

No. 7 Falmouth (11-7) advances to Saturday’s Class A South regional semifinal at No. 3 Scarborough (13-4).

Last season Falmouth knocked off No. 1 South Portland in the quarterfinals.

“People keep underestimating us. We have a great group of guys, great coaching and no one believes we can do it but us and that’s what we keep saying,” Kiely said.

Thornton had won 10 straight games (12 counting its win in the SMAA championship tourney), making a habit of winning close contests. Their last three regular-season wins were by one run, including a 3-2 defeat of Falmouth. Senior shortstop Tim Smith and his teammates expected to respond to Kiely’s home run.

“Of course,” Smith said. “We have the skills to do it. We have the energy. I thought for sure we’d get the energy back on our side and get rolling. But they made good plays. We hit the ball hard.”

Thornton sent its 3-4-5 hitters to the plate against Tracy in the seventh. Cam Seymour’s hard grounder was right at second baseman Brady Coyne. Smith’s sharp grounder was snagged on a hop by third baseman Josh Lefevre who made a strong throw to first. Tracy, who retired all six batters to get the win, finished things by striking out Calvin Christoforo (2 for 4, RBI) with a nasty 2-2 curveball.

Tracy started the year on the junior varsity but threw seven effective innings in the May 27 loss to Thornton.

“I knew I could do it. I’ve got these guys behind me, they’re playing such good defense,” said Tracy, the younger brother of Falmouth’s senior ace Garrett Tracy. “I knew I could throw against them. I knew they weren’t going to smash me so I just had to go out there, be confident and throw strikes.”

Thornton outhit Falmouth, 10-5. Falmouth scored two runs in the third without a hit (four walks off starter Luke Chessie, a throwing error and a sacrifice fly by Garrett Tracy) and two more in the fifth when Thornton made three errors. Leadoff hitter Sam Kidder, who had two hits and two walks, scored two of the runs.

Thornton responded immediately both times. In the third the Trojans scored three runs with a two-out rally against Falmouth’s freshman starter Bennett Smith. Seymour smoked a double to deep center, Tim Smith walked and Christoforo drove in the first run with hard grounder up the middle. Cameron Cross followed with a two-run triple to deep right.

After Falmouth regained the lead, Tim Smith led off the fifth with a double and scored on a two-out single by Toby Pydych to tie the game.

While he gave up some hard-hit balls, Bennett Smith stranded seven runners in his five-inning effort.

“Two freshmen pitchers,” said Falmouth Coach Kevin Winship. “The way this season went with the rain and everything we had to use them and they proved time and time again that they can play and they can pitch.”

Now Falmouth can come back with Garrett Tracy against Scarborough. “We live to play another day,” Winship said.