This could be Gary McKnight’s best coaching season at Mater Dei

How does a basketball team lose all five starters to graduation, then make it back to the Southern California regional championship game a season later?

That’s the extraordinary accomplishment Santa Ana Mater Dei (30-3) has pulled off in what might be the best coaching job in Gary McKnight’s 29 seasons.

McKnight is the winningest coach in California prep history with a record of 890-81, and the Monarchs’ 72-55 rout of the supposedly invincible Long Beach Poly Jackrabbits in a Division I semifinal Saturday will surely rank as one of the most meaningful victories in school history.

“It reminds me of the Fairfax win [in 1987],” McKnight said. “I still remember that, and I can’t remember what happened yesterday. Losing 11 seniors and five starters, I never thought I’d be back in the SoCal finals.”

In 1987, Mater Dei defeated unbeaten Fairfax, 46-42, in the regional final, and McKnight proclaimed, “This was the best win ever.”

Twenty-four years later, he might have to revise his thinking. Poly was 31-1, with size, experience and toughness. The Jackrabbits did what all favorites try to do — go for a first-round knockout, opening a 19-6 lead on the Monarchs. But Mater Dei’s youth became an advantage. The Monarchs didn’t crumble — they fought back and never let up.

Yes, the arrival of Xavier Johnson from Temecula Chaparral this season provided a big boost to the Monarchs. But this team got much better because of the steady improvement of players who were pretty much forgotten on last season’s team that won a Southern Section Division 1AA championship but lost to Westchester in the regional final.

Junior Katin Reinhardt, a USC commit, has become one of the most versatile players in the Southland. Guards David Brown and Eli Stalzer, plus football player Josh Cook, have been steady, reliable contributors. Freshmen Stanley Johnson and Shaqquan Aaron keep delivering when asked, and sophomore Jordan Strawberry is developing fast.

It all means that Saturday’s Division I regional final at USC’s Galen Center between Mater Dei and Corona Centennial ought to be an entertaining, fast-paced affair. Centennial beat the Monarchs, 60-58, in a 1AA semifinal when its full-court pressure defense produced some rare panic moments by Mater Dei in the second half.

McKnight will have a week to prepare for the press.

This was supposed to be the week Poly played Woodland Hills Taft, the City Section champion, for a trip to Sacramento.

Instead, two teams that have begun to play their best basketball are set to meet, with the winner in excellent position to take home a state championship.

Coaching achievements

McKnight isn’t the only coach having a good season. Josh Giles at Centennial has a team with no starter taller than 6 feet 4, and the Huskies keep winning with hustle, terrific defense and out-of-this-world shooting.

La Canada’s Tom Hofman has spent 25 years teaching fundamental basketball, working with whomever showed up at his neighborhood school, and now the Spartans are one win away from playing for the Division III title.

Miguel Villegas at L.A. Windward scheduled a bunch of tough teams during the regular season, and his squad took its lumps, but look where the Wildcats find themselves, playing for the Division IV regional title.

Andre Chevalier, well-known for his coaching days at Reseda Cleveland, where he tutored Nick Young, has Westlake Village Oaks Christian in the Division IV regional final. It’s just the beginning of the Lions’ rise to basketball prominence.

Eric Cooper of La Verne Lutheran didn’t know until the last minute whether his team would be invited to the state Division III playoffs. After wins over Orange Lutheran and North Hollywood Harvard-Westlake, the Trojans only need to defeat La Canada for a trip to Sacramento.

eric.sondheimer@latimes.com