By their own accounts, Duxbury High juniors Mary Buckley and Grace Ali have done everything together throughout their childhoods.

They’ve done homework together, stayed at each other’s houses, but above all else, they’ve been swimming side by side for years. That’s been the foundation of their friendship.

“Mary pushes me to continue excelling in my events,’’ said Ali, “and I do the same for her. It’s great to have someone there at your lane, always cheering you on no matter what the circumstances may be.’’

“They’re practically fish friends because they’ve always loved being in the water,’’ said Anna Jamieson, another junior on the Duxbury girls’ swimming team. “Some of their best memories come from the pool.’’

Perhaps the best came last February at the 2016 Central/South Girls Swimming and Diving Sectionals.

Duxbury was down, 187-182, to Hopkinton, with the 400-yard freestyle relay looming as the last event.

To win the championship, coach Elizabeth Walsh told the swimmers, they needed to take that relay. Buckley started off and swam well, tying her Hopkinton rival. It was a tight race, with Hopkinton taking a two-second lead as the final swimmers took off.

Fortunately for Duxbury, Ali was the anchor. She kept it close for the first 50 yards, then kicked it into another gear and finished the race three seconds ahead of her Hopkinton opponent.

Once she came out of the pool, Buckley was the first to hug her. They watched as the final tally hit the scoreboard: Duxbury 222. Hopkinton 221.

“This was my favorite moment so far in my high school swimming career,’’ Buckley said. “Just seeing everyone’s reactions after we won was priceless because we had won back-to-back titles.’’

Ever since their first day on the team, Walsh knew there was something different about Buckley and Ali. Within their first few meets, they showed Walsh they could be leaders and dominating swimmers for the next four years.

The two fully emerged at last year’s sectionals and state tournaments. Buckley placed first in her favorite event, the 100-yard breaststroke, during the sectionals and state tournaments. She was also less than a second away from breaking two meet records and a state record — her goal for this season.

Ali took first place in the 100-yard butterfly and freestyle during sectionals and finished second in the state tournament. Her goal is to reach that top spot across the board this season.

“It’s great to set your own individual goals before the season, but you need to focus on the team too,’’ Ali said. “We truly believe that we have a team that can win not only another sectionals championship, but bring home the state championship too.’’

Buckley and Ali can help prepare teammates for pressure environments, but they also communicate the main ingredient Walsh wants — a love of swimming — with their smiles every time they jump into the pool.

The two are trying to perfect their craft by swimming with Kingfish, a club team based in Kingston.

With the duo and Jamieson still juniors, Walsh has much to look forward to this season and next. When those three graduate, Julia Ali, Grace’s younger sister, will likely step into a leadership role. She has been swimming with Grace since elementary school, and has already broken two Duxbury High records.

“I hope to continue learning from [Grace] and Mary for the next couple years,’’ said Julia Ali, “and hopefully I can swim with as much passion as those two when I’m an upperclassman.’’

For the moment, though, the College Swimming website ranks Buckley (number three) and Grace Ali (number five) among the top five female swimmers in the Massachusetts class of 2018. They say they’d love to continue swimming side by side in college, but don’t know what the future holds in that regard.

Their coach envisions potential college scholarships for each.

“I’m fully expecting to be seeing Grace and Mary and planning to go see them in their college meets at a really solid strong Division 1 program,’’ said Walsh. “I’m so proud of what these two have been able to do so far, and I’m excited to have them for a couple more years.

“With every minute that passes by, their futures are looking better and better,’’ she said.

brian.mozey@globe.com@BrianMozey