St. Joseph proved to be dragon slayers throughout the Class S girls lacrosse tournament, until the 15th-seeded Cadets met their match in the third-seeded Somers High Spartans in the state semifinals at Fontana Field in Southington on Tuesday night.

Somers triumphed 12-10 to advance to the finals on Saturday at Jonathan Law in Milford. Somers (16-3) will play fourth-seeded Canton High (16-3), after the Warriors knocked off top-seeded Old Lyme 15-11 in the first semifinal.

Amanda Lopez scored five goals for St. Joseph (11-9). Susie Vazzano tallied a pair. Annie McNeil, Lindsay Lucifora and Robyn Pelletier scored one goal each.

Somers was led by Danielle Hollister, who scored four goals including one with 4.9 seconds remaining in the first half to tie things at 5-5.

Marianne Dalessio and Madison Renaud each found the net three times.

St. Joseph took a 3-0 lead in the first 4:28 of the lightning-delayed match. Lopez, a junior, scored twice and McNeil, a freshman, had the other goal.

Cadet goalkeeper Emily Buccigross stonewalled Dalessio to keep the lead, before the Spartans ran off three straight goals of their own. Two of the goals came during a four-minute player advantage.

With the sides even, St. Joseph's Carly Michalka forced a turnover in the defensive end and Lucifora challenged Somers in transition. The senior hit a post, but classmate Pelletier collected the carom and reset the attack.

A pushing foul gave Lopez a free position attempt from 12 yards out, and she scored low and to the outside of Somers’ netminder Laura Morton.

St. Joseph led 5-4 with four minutes remaining in the half.

Christina Psaras gave St. Joseph a chance to pad its lead when she won a ground ball at midfield and fed Pelletier, who worked her way around the frame before her shot hit off the top bar.

The Cadets, led by Michalka, Psaras, Grabowski, Samantha Dyson, Lucifora and Mikaela Trafecante, used a stellar zone defense to slow the Spartans down, but Hollister’s free-position tally forged a tie at intermission.

St. Joseph, which had unforced errors in the first half, forced a couple of turnovers of its own early in the second session.

Grabowski got a takeaway at the defensive end, after the draw went to Somers.

Lucifora’s shot was deflected wide, but Kate Condron was there to win a battle for the loose ball.

Patiently running their offense, the Cadets struck when Abbey Ivanovich found a cutting Lopez for the score and a 6-5 lead at the 23:22 mark.

Pelletier won the draw and had her shot stopped by Morton.

Looking to transition quickly, Somers was stopped when Vazzano came away with a steal.

The senior had a chance on the near side, but it would have been from a tough angle. She kept possession, worked around the cage, and then deposited a shot at 22:07 for a 7-5 lead.

After playing a near perfect three minutes, the Cadets saw the Spartans show their mettle.

Somers scored goals at 18:31 (free position), 18:07 (turnover) and 15:35 to take an 8-7 lead.

Another penalty on St. Joseph gave Somers an extra attacker and Ashlie Delskey scored at 14:16 for a 9-7 advantage.

The Cadets hit their third post at the 13-minute mark and Buccigross had two saves, including a dazzler on Delskey from point-blank range with 11:16 remaining.

Pelletier was robbed of a goal by Morton one-minute later.

The Cadets pressed on, as Lopez turned Somers over and then rode off the hip of a defender to beat Morton at 8:26.

The Cadets won the draw and had possession with a chance to tie, before the Spartans’ Catherine Thresher stole a pass and fed Hollister going away for a two-goal lead with 7:34 on the scoreboard.

Somers scored on two straight possessions to extend the lead to three, before McNeil found Vazzano open to make it 12-10 with 1:51 remaining.

The Cadets had two shots go wide in the final minute.