Backup Andrew Katnik steps up to lead St. John Bosco to victory

Its standout quarterback, Josh Rosen, was on the bench with his right arm in a sling. The scoreboard showed a 28-10 deficit. Yes, No. 1-ranked Bellflower St. John Bosco was facing a major test of character Saturday against Chandler (Ariz.).

Unsung backup quarterback Andrew Katnik, taking deep breaths while trying to calm his nerves, guided four consecutive scoring drives to rally the Braves (3-0) to a 52-31 victory in the Mission Viejo Classic.

Katnik completed 10 of 11 passes for 121 yards and two touchdowns. Sophomore Sean McGrew broke off an 88-yard touchdown run in the fourth quarter to prevent any Chandler comeback. Rosen, one of the top junior quarterbacks in the state, injured his shoulder in the second quarter after a roughing-the-passer penalty. He plans to undergo an X-ray to determine the seriousness of the injury.

“Andrew is a fully capable starting quarterback in the Trinity League,” Coach Jason Negro said of the senior. “However long Josh is out, Andrew will be able to perform.”

Said Katnik: “When I first got out there, I was a little nervous, but after that first series, I calmed down, made the throws, made the reads.”

Chandler junior quarterback Bryce Perkins was impressive. He completed 26 of 36 passes for 267 yards and one touchdown and ran for 118 yards and one touchdown.

Streak buster

Corona Centennial’s offense had put together a streak of gaining 400 or more yards in 44 consecutive games dating to the 2010 season. That came to an end Friday night, when Long Beach Poly held the Huskies to 287 yards in Poly’s 35-28 victory.

Just last week, Centennial (2-1) gained a school-record 886 yards against Ventura St. Bonaventure and Tre Watson rushed for a school-record 466 yards. Against Poly, Watson was held to 48 yards in 23 carries.

“Our plan was to blitz all the gaps and not let him get through the line without being hit,” said Poly safety John Smith. “If he did get through, contain him and make sure you make the tackles. He’s been running like crazy on everybody, but I think we did good slowing him down.”

Said Centennial Coach Matt Logan: “The running game wasn’t working, and that’s partially on us and partially on them. They certainly bottled us up and made plays, but I think our execution and timing was off at times.”

83 points

Loaded with talented sophomores, Sylmar set a school record for points with an 83-42 win over Verdugo Hills. Sophomore quarterback Clarence Williams accounted for eight touchdowns, seven on passes.

Town sidelined

St. Bonaventure quarterback Ricky Town sat out the Seraphs’ 35-13 victory over Redlands East Valley because of a hyperextended knee. He’s not expected back for a couple of weeks.

Sophomore Darius Vines is filling in.

Inland power

A year ago, Rancho Cucamonga went 10-3 and got lots of attention because of two high-profile recruits, Chris Hawkins (USC) and Tahaan Goodman (UCLA). But this year’s team could be better.

The Cougars are 3-0 after a 32-29 win over La Puente Bishop Amat in which quarterback Gage Pucci passed for 278 yards and four touchdowns.

Rising teams

Trabuco Hills (3-0) could be emerging as a playoff contender from the South Coast League after its third consecutive nonleague victory, a 24-17 triumph over Fountain Valley....Sophomore quarterback Eric Barriere had five touchdown passes to help La Habra (3-0) defeat St. Paul, 41-7.

eric.sondheimer@latimes.com