You would have never guessed from watching Sierra Brophy play that she spent all year running with the Massapequa junior varsity squad.

The freshman, thrown from junior varsity into a prominent role at forward after injuries to key Chiefs playmakers, scored two goals in No. 1 Massapequa’s 5-2 win over No. 5 Syosset on Friday in a Nassau AA girls soccer semifinal game at Cold Spring Harbor High School. Hope Breslin, last season’s Newsday Player of the Year, also had two goals.

“This girl comes up from JV and I have to check to make sure she’s really in ninth grade,” coach Bruce Stegner said, “because it’s pretty impressive stuff.”

Massapequa (14-1-2) will play No. 2 Calhoun (9-3-5) — which won, 1-0, in the second game — Tuesday at Cold Spring Harbor High School at 4:30 p.m. as the Chiefs look for their fifth straight Nassau AA title and 13th in 14 years.

Syosset (3-6-4) scored first against the three-time defending state champions when Tejan Singh finished a corner kick from Rachel Rosenberg with 20:51 remaining in the game. But the Chiefs didn’t panic from a rare deficit.

“We knew that if we played our game, we’re a really good team and we’d be able to beat them,” Breslin said. “So we just had to stay calm.”

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Brophy scored the tying goal off a cross from Julia Ophals with 7:58 remaining in the first half.

Syosset’s Lauryn Shin’s penalty kick goal with 4:35 left in the half.

Breslin pulled off an impressive header for a goal off a corner from Kyleigh Gallagher with 20.6 seconds left, tying the score at halftime.

But it didn’t remain tied for long out of the half as Brophy scored off a steal from 25 yards to give the Chiefs a 3-2 lead with 32:41 left in the game — with Breslin firing a goal from 35 yards and Cassidy Byrns adding a goal in a span of 4:30 to make it 5-2.

“It was really fun,” Brophy said. “I look up to all the girls on the varsity team to keep me going when I make mistakes, so it was really helpful to have them.”

And Massapequa’s relying on players such as Brophy with the goal of winning a fourth straight state championship.

“We’ve made it every single year and it would be such a disappointment to end the streak,” Ophals said. “We’ve come so far and worked so hard and it would just be a really great ending.”

In the nightcap, No. 3 Port Washington and No. 2 Calhoun played a much different match than when each team won 3-2 contests in the regular season.

After a scoreless first half, Annie Coogan kicked in a cross from Kathryn Healy with 20:26 remaining in the game in Calhoun’s 1-0 victory. Gillian Stapler had a strong game in net, finishing with 10 saves.

Coogan continued her series of heroics after the winning goal in a 1-0 quarterfinal win and she also scored the winning goal against Port Washington in the regular season.

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“It’s crazy,” Coogan said. “It felt like her pass was meant for me, like she knew where I was going before I even got that.”