The kid had forgotten his shoes. He was a co-captain of the Martha’s Vineyard Regional High School tennis team and the team was playing one of its final contests of the season, an away match against Duxbury. He had no choice. He asked head coach Ned Fennessy the only question possible: What size shoe do you wear?

No matter that the forgetful captain was a size 10 and Mr. Fennessy an 11 and a half (double E). The pair switched shoes, the player lacing up the oversized sneakers, and the coach resigning himself to “hobbling around the courts” in a pair of far-too-small flip-flops.

“So you do what you have to do sometimes,” Mr. Fennessy said, smiling. “And of course he went out and lost.”

But looking back at Mr. Fennessy’s 22 years as head coach of the tennis team, losses stand out as the exception, not the rule. The team has had just three losing seasons since he came on board in 1991 (in 2008, they were 9-9, which still qualified them for the postseason).

This year, the Vineyarders are undefeated for the first time ever, sporting a perfect 18-0 record as they head into the Massachusetts Interscholastic Athletics Association Division 3 tournament as the number one seed. They took the Eastern Athletic Conference League championship title for the third year in a row. The entire starting lineup — juniors Kent Leonard, Patrick McCarthy, Justice Yennie, Jackson McBride, Natty Schneider, Justin Smith and Ryan Sawyer—was named to the EAC All-Star Team.

In April, Mr. Fennessy recorded his 250th win with the team. He’s nearing a milestone of a different sort as he approaches his 80th birthday.

“It’s pretty special,” he said of the unprecedented success.

The team needed a coach. Jay Schofield, renowned basketball coach and physical education instructor at the high school, thought of his friend Ned, a retired industrial engineer who split his time between the Vineyard and Sarasota, Fla. Ned’s Vineyard connections went back to the 1880s, when his great-grandfather built the Hotel Naumkeag in Oak Bluffs. He’d grown up in Yarmouthport, but visited the Island often; in 1970 he and then-wife Nancy decided to buy a home here.

He’d started playing tennis early, influenced by his father, Frank, who played with the national doubles team in the 1920s. Ned was a co-founder of the Chamberlain Pines Tennis Club in Holliston, a a club player himself who never had the chance to play in high school or college simply because tennis wasn’t offered then.

So he had “kind of freelanced,” deciding in the 1970s to start Chamberlain Pines with his club doubles partner Kenneth Ghelli, a native of Holliston. They bought 11 acres in town, built six courts and a clubhouse, and took an 18-hour course at Harvard on tennis instruction from Crimson coach Jack Barnaby (then only in his fourth of seven decades as coach) so they could teach at their new club.

The endeavor was a success — indeed, Chamberlain Pines has expanded considerably since the 1970s—although a short-lived one for Ned: in 1975 he was transferred to Minneapolis by the company he worked for, Honeywell. He remained in Minneapolis, continuing to freelance teach until his retirement in 1990, when he returned to the East Coast. And before the 1991 tennis season began at the regional high school, he took Mr. Schofield’s suggestion and put in for the coaching job.

“And I got the job,” he said, drawing out the pause before the kicker, “because I was the only applicant.”

He planned to stay for four years, long enough to see a freshman class move through the ranks.

The team needed players. Mr. Fennessy had set up a team meeting before that first season started, walking into the room to find three kids waiting for him. He was reassured that two more players were on their way, but that still fell short of the seven needed to start a tennis match. A few more athletes were recruited to the cause, and the Vineyarders were on their way.

They went 5-7 that first year, and 2-11 the second. But eight of the eleven losses had been close 3-2 defeats, and Mr. Fennessy could see the players improving. In 1996, just five years into his tenure, the team went 13-1, sharing the co-championship of the Cape and Islands League with then-powerhouse Nauset — “a significant accomplishment for the kids and me,” he said.

Player shortages are no longer an issue, not since the inception of the Vineyard Youth Tennis Center 10 years ago. The center, which offers free lessons and year-round tennis to players under the age of 18, allows tennis athletes to not only work on their game throughout the off season, but also to begin developing their skills at a younger age.

“That makes all the difference in the world,” Mr. Fennessy said. “The people that started the center and the pros that teach there have as much responsibility for this team’s success as I do.”

How do you coach tennis? There’s no physical contact in the game, but the sport is nevertheless a brutal one by nature of its simple isolation — there are, as Mr. Fennessy points out, no substitutions in tennis.

“To me, it is one of the most difficult sports to master,” he said. “Not only do you have to develop the strokes, but you have to be an athlete. And when you play tennis and you’re out there, you’re out there by yourself.”

So he teaches the players not only how to serve and run down a ball, but also how to think. How to change the course of a game by making your opponent overthink.

“If you wind up [against] a player that’s physically and tennis-ability-wise equal, the one that’s going to win is the one that’s going to think better on his feet,” Mr. Fennessy said.

But the players have to perfect their tennis abilities in the first place. The game “has changed tremendously from when I first started,” said Mr. Fennessy—the style of play shifted from serve-and-volley to baseline, the strokes became more powerful, the rackets became (literally) less wooden.

“The power that the kids can now master is huge,” he said. “And that’s all to the good.”

Practices typically consist of group drills followed by a playing session. This year, Edgartown Yacht Club head tennis pro Paul Pertile has come on board to help out — “with significant accomplishment, because I’m slowing down,” said Mr. Fennessy, laughing.

Mr. Fennessy was awarded coach or co-coach of the year by the Cape and Islands league four times. In 2009, the same year his team advanced to the MIAA South Section semifinals for the first time, he was named Division 3 Coach of the Year by The Boston Globe.

He set three goals for the team this year, though the three are interrelated in their combined challenges to the players to be the best they could possibly be. The Vineyarders have already won their conference, and they’ve also earned the MIAA Academic Achievement Gold Certificate for having a cumulative GPA of 3.23. Eleven of the 16 players are on the honor roll; four earned high honors. This is the second year in the row they took the gold certification (in 2007, the starting seven had a cumulative GPA of 3.7, Mr. Fennessy said, “which was exceptional” even by the high tennis-team standards).

The third goal is to win the MIAA Division 3 South Section Final, which slipped just out of the team’s grasp last year at the hands of Cape Cod Academy. For all of their successful seasons, the 3-2 loss to CCA was the closest the Vineyarders have ever come to the title of South Section champion.

But this team, this literal All-Star group of athletes, is “the best team I’ve ever had in total, no question,” Mr. Fennessy said. People have asked him why he doesn’t create a stronger schedule for the Vineyarders, but he tried. In addition to the Cape Cod Academy matches, he pitted the team twice against Dover-Sherborn (who thwarted the first attempt at reaching the sectional final four years ago) and newcomers Quaboag and Randolph. The Vineyarders beat them all; the match scores against Cape Cod Academy were 3-2, but skewed, for once, in favor of the purple and white.

Still, the new and old opponents are fine teams, Mr. Fennessy said, emphasizing, again, the narrow 3-2 margin of victory. There will be no resting on laurels this postseason.

Besides, playing a weaker team allows him to start players who are not part of the main lineup. All 16 members of the team have seen varsity time this season, playing in at least one match, a facet Mr. Fennessy considers equally as important as winning.

The coach will turn 80 soon. He’s taking things “a year at a time,” he said, and intends to come back next year. He wants to see the team at its peak, as seniors, to see how well they can do.

The original plan, of seeing a team all the way from freshmen to graduation, hasn’t really changed much.