Cam MacDonald is in the midst of his finest season on the diamond at American International College. Yet a shining moment from his senior year at Weymouth High still resonates with MacDonald and two of his former teammates, the final out of their victory over Braintree four years ago to clinch the Bay State Conference’s Carey Division title.

A team captain who played second base and took a regular turn on the mound for Weymouth, MacDonald spun a last pitch that resulted in a grounder to Brett Julian, who fired the ball to first baseman Mike Laracy to secure the win.

“We always talk about it, how cool it was for three of us to be involved in such a great moment,’’ MacDonald said of his two fellow captains.

This spring, Laracy and Julian are senior pitchers at Merrimack College, while at Northeast-10 Conference rival AIC, MacDonald is putting together terrific numbers for the Yellow Jackets as a redshirt junior.

Through 32 games, the third baseman was batting .309 (35 for 114), and pacing AIC in runs (23), on-base percentage (.433), stolen bases (12 in 16 attempts), walks (17) and hit-by-pitch (9).

He had also pitched in four games, one as a starter, compiling a 2-0 mark with one save and an 0.79 earned run average. He had allowed just four hits in 11.1 innings.

Julian, a reliever, had appeared in seven games, and Laracy, a starter, was 2-0 with a 3.92 ERA for Merrimack, 21-15 overall heading into Saturday’s game against Franklin Pierce.

“Cam is the anchor of our infield that includes two freshmen. He gives us stability and leadership,’’ said AIC head coach Nick Callini, whose team was 16-17 prior to Friday’s doubleheader against Southern Connecticut.

“He’s always fresh and ready to go on the mound, and he’s improving as a hitter after going through some injury problems. Cam is the kind of player you’d love to have nine of in your starting lineup.’’

A Bay State Conference all-star and recipient of the coach’s award his senior year at Weymouth High, MacDonald missed the 2010 season at AIC because of a broken bone in his right wrist.

“The injury took a toll on me two years ago, and then the same bone was broken again last season. I had to play through the pain and last May I had surgery,’’ said MacDonald, who despite the nagging injuries was named to the NE-10 All-Rookie team in 2011, when he hit .270 and was 2-2 with a 4.00 ERA in six games, including five starts.

Last season, he hit .264 and was 1-2 as a starter with a 4.11 ERA

Thanks to a rigorous offseason workout schedule that included weekly visits to Cressey Performance in Hudson, the 5-foot-9, 180-pound MacDonald said he is stronger, quicker, and “in the best shape of my life.’’

He learned how to field as a youngster with the help of his father, Ed MacDonald, who would throw grounders and fly balls to him in their yard.

“There was a downslope and some woods I had to deal with, but I made a few tough catches, it was great fun and a big reason baseball became a passion for me,’’ said MacDonald, who along with Laracy and Julian led Weymouth to a 14-8 record their senior year and to the South sectionals for the third consecutive season.

The team, coached by Tony Green , received the Division 1 baseball Sportsmanship Award from the Massachusetts Interscholastic Athletic Association. Julian was the league MVP.

“We were the team’s three pitchers when we weren’t playing in the field, and we’re still best of friends,’’ said MacDonald, who had a hit in each of the four games that AIC has played this season against Merrimack. The Yellow Jackets won three.

“I’ve always loved both sides of the game — hitting and pitching — and I’m a pretty patient batter who tries to draw walks and get pitchers deep into counts,’’ said MacDonald, a natural righty who bats from the left side.

“Honestly, I never thought of myself as a base stealer, but being stronger and healthier has given me the confidence to be more aggressive on the bases, and to try to get in scoring position.’’

MacDonald plans to return to the team next season as a graduate student, and Callini, who arranged for his partial scholarship two years ago, said he’s welcome to join the coaching staff two seasons down the road.

“With Cam,’’ said Callini, “you never worry about his commitment to the game or doing what he needs to succeed.’’

Area athletes earn conference honors