Katie Rorem and Carsen Harkins were fifth graders the last time Mercer Island lost a girls golf dual match.

They no doubt were as oblivious as their classmates at the time. Harkins, in fact, didn’t golf back then. For Rorem, it was a family sport that took second fiddle to soccer.

They didn’t take note when the Islanders went unbeaten the following year and the year after that, although Harkins had taken up the game by then. But by the time they were freshmen, they realized they could be part of something special.

And they have been.

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Now senior co-captains, Rorem and Harkens have helped the Islanders (11-0) stretch their unbeaten streak to 75 matches — which ranks seventh nationally, according to the National Federation of State High School Associations, and is the No. 1 active streak. Hingham Notre Dame Academy in Massachusetts had its record 188 unbeaten stretch end last May.

A win Thursday in the season finale against Bellevue would put Mercer Island in a tie for sixth all-time.

But that won’t come easily. Bellevue is also undefeated this season.

“They could beat us,” MI coach Don Papasedero said candidly.

Mount Si nearly ended the streak last Wednesday, as MI won on tiebreaker criteria. As the scores were being tallied, it became apparent how close they were.

“That was frightening,” Rorem said.

In the end, MI’s depth prevailed. It has been a strength of the program Papasedero started in 1998 at the request of the late Gary Adrian, then the boys golf coach at the school. Papasedero’s passion is coaching football, which he has done at various stops since 1974.

But he was looking for a spring sport to coach, and he enjoyed golfing, so he figured why not? The Islanders went 7-0 that season, winning the first of nine KingCo titles, and are 160-20 during his tenure. They won the 3A state championship in 2011 and have six top-eight finishes.

Papasedero credits golf instructor Tim Okamura for much of Mercer Island’s success the past six seasons, as well as the team-first concept.

Players are partnered together all season. Rorem and junior Whitley Peterson, in fact, have been partners for the past two years.

“She knows what to say when I’m having a rough day, and she knows how to help me fix my swing,” Rorem said, “so I think we have a great advantage.”

Harkins, who is playing with freshman Abby Zhong this spring, likes the partner and team aspects, too.

“Golf can be really frustrating, but you have to remember you’re contributing to the overall score of the team, and I think that really helps everyone,” she said.

The sport has become popular, drawing as many as 30 girls in some years, even though there is no golf course on Mercer Island and the team plays its home matches at Jefferson Park in Seattle.

The girls wind up sharing a special bond, according to Papasedero.

“I really think they do celebrate the sisterhood and liking each other and being a team,” he said. “It sounds a little corny, but they get a big charge out of it. When you play Mercer Island, you play a team. There are no individual parts of it.”

MI’s last loss dual came against Skyline in the final match of the 2007 season.

“It’s an amazing thing to be a part of,” Harkins said of the streak. “We’re super lucky that it’s gone on for so long.”

Sandy Ringer: 206-718-1512

or sringer@seattletimes.com