LYNN  — Masconomet was good. But St. Mary’s was better.

In a meeting of undefeated Division 2 contenders Monday night, St. Mary’s defeated Masconomet, 75-61, in a game much closer than the final score indicated.

St. Mary’s (9-0) protected its home court with the victory, giving Masco (7-1) its first blemish of the season. Two keys for St. Mary’s were controlling the offense glass and hitting open threes, and with 10 offensive rebounds and a dozen threes, the Spartans excelled in both of those areas.

“Masco is a very good team, so we needed to play every single possession for four quarters,” said St. Mary’s coach Josh Keilty. “There was adversity in front of us here against a team this disciplined, so it was a chance for us to play together and get better.”

For three quarters, this game lived up to the hype. Led by senior forward John Chareas with eight points in the first quarter, St. Mary’s came out shooting, jumping ahead, 27-17, after one. But Masconomet was sensational in the second quarter, forcing six turnovers and winning the battle on the boards with eight rebounds to St. Mary’s four to turn the game in their favor. Senior guard Jimmy Farrel poured in 10 of his 26 points in the second quarter, cutting the deficit to one as St. Mary’s clung to a 36-35 halftime lead.

Yet this was the tale of two halves. Keilty, who has been preaching defense since the moment he was hired over the offseason, orchestrated a masterful plan to prevent Masco from getting second-chance scoring opportunities, or, for that matter, open looks. A critical part of that was the defense of junior Rowan Merryman (4 points, 5 rebounds), who took pride in limiting Farrel’s offensive output.

“This was a group effort,” said Merryman. “Masco is a tough team, so we stuck to our assignments on defense. Offensively, we had to move the ball to win, so it was important to be unselfish with the ball and find open shots.”

With St. Mary’s ahead 57-49 entering the fourth, it was a collective effort that prevented Masconomet from building enough momentum to get back in the game. And though the Chieftains trimmed the lead to six with 3:07 to play, it was St. Mary’s post player Gabriel Makuwa-Sykes (16 points, 7 rebounds) who drilled a three on the very next possession to extend the lead back to nine.

“We came out ready to go, but in the end, we just didn’t have enough juice in the tank in the second half,” said Masconomet coach Jaycob Morales. “These were two great teams battling it out, but we need to be better. We play two more times this week, so we need to get our rhythm back.”

Jake Fortier (17 points) and Rolky Brea-Arias (19 points, 12 rebounds) both contributed to the win.

“Coach Keilty and our coaches put a lot of faith in us,” said Brea-Arias. “We like defense better than offense. That’s our yard. That’s where we need to better than everyone else if we’re going to win. This was a good win, but it just means we need to keep working.”

The starting five for St. Mary’s accounted all but one point, and that group continues to excel together on the court this season.

“Playing at St. Mary’s is everything I imagined and more,” said Chareas, who is a transfer from Manchester-Essex. “Coach Keilty really brings the best out of us, and I love playing with my teammates. It’s a versatile team, and we are who we are because of our defense.”