HUDSON — The Groton-Dunstable softball team was familiar with the venue, but knew little about their opponent when they traveled to Hudson to tangle with Nipmuc Regional in the Central Massachusetts Division 2 Softball Tournament semifinals at Hudson High School.

But the Lady Crusaders used their standard formula and advanced to the finals with a solid 4-2 victory. Junior lefthanded pitcher Jess Sullivan tossed a complete game five-hitter, supported by flawless defense as the third seeds knocked off the second seed. O’Sullivan used her moving fastball to advantage throughout the contest, consistently getting ahead in the counts and striking out 13 and walking one.

“Jess is phenomenal,” said Groton-Dunstable coach Derek Asadoorian. “She makes it happen, but she is surrounded by a good supporting cast. Of the four categories, we were good in three today. We got good pitching, solid defense and we hit the ball well. We did not do a good job of running the bases.”

The first two innings were scoreless. Groton-Dunstable threatened in the top of the second when Breezy Riposa led off with a long double to right center, but Nipmuc pitcher Becky Tiernan bore down and retired the next three hitters to escape unscathed.

Brittany Ernst led off the bottom of the first with a bunt single for the Warriors, but was gunned down trying to steal second base by Groton-Dunstable catcher Kate Stowell. Hayley Davidson walked to lead off the bottom of the second and stole second, but O’Sullivan struck out the next three hitters to keep the game scoreless.

The Lady Crusaders broke through in the top of the third, making good use of small ball. Kiersten Bieren led off with a bunt single, and Megan McLean’s bunt single put runners on first and second. After a double steal, Stephanie Dodson delivered a sacrifice fly to plate Bieren. O’Sullivan singled and Kerry Alcott reached on an error to load the bases before Riposa (sacrifice fly) and Kate Stowell (single) brought home runners to make it 3-0.

The Lady Crusaders appeared primed to add to the lead in the top of the fourth, but were denied by an outstanding defensive play by the Warriors. With two outs, McLean singled. Dodson singled to right, but rightfielder Brianna Muise’s perfect throw to third nailed McLean for the third out.

O’Sullivan was on cruise control, retiring 12 consecutive hitters from the second to the fourth. She struck out eight hitters over that span with just two balls leaving the infield, both fly balls hauled down by Dodson in center field.

Groton-Dunstable continued to put runners on base, but frittered away chances to pad the lead.

In the fifth, O’Sullivan reached on an error and Alcott singled to open the inning, but Nipmuc catcher Davidson tossed out O’Sullivan trying to steal third, and Tiernan retired the next two hitters to keep it a three-run game. At that point, Groton-Dunstable had eight of the nine hits in the contest.

After the Lady Crusaders were retired in order in the top of the sixth, Nipmuc broke the ice in the bottom of the inning. Muise and Janine Perro led off the inning with singles. After O’Sullivan got a flyout and strikeout, Brianna Sarcione’s sharp single plated Muise and put runners on the corners. O’Sullivan reached back and struck out the clean-up hitter to send the game to the seventh with the Lady Crusaders on top 3-1.

Groton-Dunstable got that run back in the top of the seventh when McLean singled and scored when Alcott hit into a fielder’s choice.

Nipmuc didn’t quit and Casey Rhodes homered just inside the left field foul pole with one out in the bottom of the seventh, but O’Sullivan notched a strikeout and induced a foul pop-up to Stowell to end it.

McLean paced the offense with three singles and two runs scored. Stowell turned in a strong defensive effort behind the plate.

“Meg did a nice job out of the leadoff slot in setting the table for the offense,” said Asadoorian. “We did a nice job of playing small ball. We hit the ball well in the game and made a lot of loud outs. Also, we played with a tighter strike zone than we were used to. This is the furthest we have ever advanced in the Districts and we are looking forward to playing in the championship game.”