When Sachem East upset top-seeded Ward Melville in last season’s Suffolk AA girls basketball quarterfinals, there weren’t necessarily shock waves sent through the county.

But it did put teams on notice. It signaled that Suffolk League I was a force to be reckoned with.

The Flaming Arrows were the No. 8 seed and boasted a young core, headlined by Danielle Cosgrove and Gabby Aspuru, now a junior and senior, respectively. Ward Melville was a team they knew all too well after the Patriots beat them twice during the regular season in league play.

The budding rivalry between the two teams is perhaps the focal point of what’s expected to be a compelling season in Long Island’s toughest league.

“League I is by far stronger than the rest of the leagues,” said Cosgrove, a 6-4 center with shooting range that extends beyond the arc. “That’s not a knock on anyone in those leagues, but we play with a certain intensity that most teams can’t really match. We practice with that intensity, and we play with it.”

Ask anyone associated with Suffolk League I to describe the depth of the league, and you’ll be met with a flurry of headshakes, anxious laughter and sheer disbelief.

Last season, Suffolk League I produced both the county champion — and eventual Long Island champion — in Commack and the county runner-up in Sachem East. Ward Melville was considered one of the county’s best and Brentwood and Longwood put together playoff seasons. The prevailing wisdom is that the league will be a gauntlet again this winter.

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“Last year, League I kind of emerged as the powerhouse league,” Commack coach Denis Conroy said. “Coming into this season, that seems to be a pretty good appraisal of where we’re at right now.”

Section XI teams must produce a .500 record or better in league play to compete in the playoffs, and in an eight-team league, some squads could have problems reaching that mark.

“If we can survive the regular season and get to the playoffs, we feel like we are definitely playoff ready,” Brentwood coach Chris Harrison said. “We feel like we’ve already had four or five playoff games by the end of the year.”

“Survival” is the operative word many coaches use when describing the trial that is Suffolk League I. Even the top teams are at risk in a league in which any team can win on any given night. Sachem East’s upset of Ward Melville last year being the primary example.

Picking a favorite to win the league might be a fool’s errand, but some coaches believe Sachem East’s balance and experience give the team an advantage. Nobody graduated from last year’s storybook season, and newcomers to varsity have shown promise early.

Ward Melville returns senior Taylor Tripptree and sophomore Lauren Hansen, a point guard who missed all of last year after ankle surgery. She’s being recruited by the likes of Florida and Ohio State, among others, according to coach Bruce Haller.

“The talent other teams have brings the level of competition up higher,” Hansen said of the individual playmakers of Suffolk I. “Everybody’s a challenge.”

It’s best not to overlook Commack, winners of the last two Suffolk AA titles. Senior Jillian Spagnuola and junior Casey Hearns bring speed and athleticism to the table for the Cougars.

Longwood’s Zorria West, Sachem North’s Annie Keenan and Brentwood’s Ty’Zhea Hawkins and K’anndra Rhoden also are versatile playmakers capable of taking over games at Long Island’s highest level.

“Any given night, somebody can step up and have a huge game,” Cosgrove said. “League I never has a short roster. Teams always have something different to throw at you.”

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And perhaps that’s what makes this league so difficult to predict. Good luck trying.