KITTERY — Sierra O’Brien knew where she had to be. And now the Traip Academy field hockey team is going back to where it wants to be.

O’Brien, a senior forward, scored a goal in each half and the third-seeded Rangers played their most complete game of the season, downing No. 6 Dirigo, 2-0, in the quarterfinal round of the Class C South playoffs on Tuesday at Memorial Field.

“That’s the best we’ve ever played, I’d have to say,” senior midfielder Kiara Perez said. “Everyone played great.”

The Rangers (12-2-1) will play at No. 2 St. Dominic Academy (12-2-1) in the regional semifinals, scheduled for Friday, weather permitting. The teams split a pair of tight games during the regular season, each winning on its home field.

It’s the challenge the Rangers knew they wanted as soon as they saw the playoff bracket, and they went out Tuesday against a team they hadn’t seen during the regular season and did their part to earn it.

“It feels really good,” said O’Brien. “I didn’t know what to expect going into it but I’m really glad we played the way we did.”

The first 23 minutes were evenly split, each team making forays toward the opposing goal. But the Rangers got the all-important first strike when Claudia Serna sent in a long pass, and O’Brien, with her basketball forward’s frame, got low to collect it on the left behind the goalie and shoot it in.

The Cougars (7-8) nearly tied the game in the final minute of the half, with freshman Grace Timberlake getting a redirection from in close. But another freshman — Traip goalie Nicole Roberts — was in position and denied it with a pad save to keep the score 1-0.

“We’ve been trying all season to get a stick on those,” Dirigo coach Gretchen Curtis said. “She gets a stick on it and the goalie makes a save.”

Even with that hairy moment late, the Rangers, who’ve started slow in several games this season, liked the first segment of their first one-and-done game.

“That was probably the best first half of a game we’ve played all season,” Traip coach Amy Cook said. “It was scoreless for a while but they had that intensity going. It felt good the whole time. There weren’t any worries.”

The second half produced even fewer worries. The first four-plus minutes were played entirely across midfield and the Rangers produced the half’s only four penalty corners, finishing with a 6-1 edge.

They cashed in for a 2-0 lead when O’Brien, set up near the left post, redirected a pass that Perez sent in from up top.

“Sierra’s been practicing on the post and she’s doing real good with that,” said Perez.

“She deserved those goals,” said Cook. “It could be the slightest tip-in, but when she’s there, in that spot, she scores goals.”

Leading scorer Amelia Sullivan had a pair of chances to extend the lead to three late but just missed. Still, it didn’t take away from the party.

“It was non-stop communication on the field,” said Cook. “Everyone was firing.”

Now comes the rubber match against St. Dom’s, after the Saints hung on against No. 7 Sacopee Valley, 3-2, a result the Rangers followed on their phones after retreating to their locker room, knowing an upset would have given them another home playoff game.

Traip beat St. Dom’s here in September, 3-1, and in Auburn in last year’s quarterfinals. It also lost a hard-fought, 2-1 decision on the road on Oct. 8.

In their last game on this field, complete with a big crowd along the fence and ceremonial balloons, the Rangers set themselves up to take the next step.

“We lost so many good seniors and the seniors now have picked it up to support the freshmen this year, because we have a lot,” said Perez. “I’m really excited for it.”