Third quarters don’t decide games, but this one was a demo model of why Punahou is the best team in the Interscholastic League of Honolulu.

The Buffanblu shut down Saint Louis’ offensive threat to begin the second half, then drove 97 yards in 12 plays and put the game out of reach in a stunningly easy 43-14 win Friday night at Aloha Stadium.

Third-ranked Punahou improved to 3-0 in league play (4-1 overall), while Saint Louis dropped to 1-1 (2-3 overall). It was a wake-up call for the Crusaders, who had averaged 46.5 points per game against elite competition.

Instead, it was Punahou’s polished spread offense that hit hard and often. Larry Tuileta was near perfect, passing for 359 yards on 21-for-25 accuracy without an interception.

Eight of his spirals went to sophomore Kanawai Noa, who had 198 yards and two touchdowns.

“They’re very talented and they run their offense effectively. That’s a great sophomore receiver,” Saint Louis coach Matt Wright said. “But a lot of it came down to having stupid mistakes, having the wrong coverages. The penalties, sometimes it’s discipline issues we’re constantly trying to remedy.

“We can’t keep putting our offense in a shootout match every time.”

Punahou’s defense was powered in part by linebacker Isaac Savaiinaea and defensive end Canton Kaumatule, both back from early-season injuries.

“The first half, we just needed to wake up. Adam (Noga) is such a great runner, we had to wake up soon,” Savaiinaea said. “Just being more patient, more violent and not overpursue.”

The Crusaders were poised to stay with Punahou point-for-point, but Noga left during the first quarter, dealing the underdogs a severe blow against the explosive Buffanblu. Wright said Noga “tweaked” a hamstring, and though the junior tried to give it a go in the second half, he wasn’t able to go 100 percent.

“We’d rather be safe than risk him being out four or six weeks,” Wright said of Noga, who finished with 75 yards on just five carries.

Coach Kale Ane’s Buffanblu went to Ryan Tuiasoa on the ground on the game’s opening series, and the senior scored on a 1-yard burst to give Punahou a 7-0 lead.

Before he got hurt, Noga scored on a 65-yard touchdown run — Saint Louis’ first play from scrimmage — up the gut and down the right sideline. That tied it at 7-all.

Punahou drove again against Saint Louis’ defense, aided by a facemask penalty, and Tuileta found tight end Dakota Torres open in the back of the end zone on third down for a 3-yard touchdown pass.

That gave the Buffanblu a 14-7 lead with 5:09 left in the first quarter.

The Crusaders tied it at 14-all on Ryder Kuhns’ 11-yard touchdown pass to Wallen Te‘o with 8:06 to go in the first half.

Punahou answered almost immediately. On the next play from scrimmage, Tuileta launched a bomb to Noa on a post route for a 67-yard touchdown, and the Buffanblu led 21-14.

They got the ball back with 3:13 left at their own 28-yard line and Tuileta went to work with precise passes — including a 32-yard strike to Keanu Chee and a 24-yard toss to Dylan Combs. Tuiasoa bounced outside to score on a 5-yard run, and Punahou led 28-14 with 1:07 before intermission.

Then came the third quarter, and the difference between the two offensive juggernauts became crystal clear. Saint Louis stumbled with mental errors — penalties — while Punahou continued to carve up the Crusader defense.

Two illegal procedure calls and a sack by Savaiinaea derailed Saint Louis’ drive. Punahou then drove 97 yards and scored on a 1-yard slant pass from Tuileta to Noa.