EUGENE, Ore. >> When  former St. Louis High School quarterback and redshirt freshman Marcus Mariota ran out on to the field at Autzen Stadium, he was nervous about his first start for the Ducks. 

By the first snap, the butterflies were gone. 

Mariota debuted for No. 5 Oregon by passing for 200 yards and three touchdowns in a 57-34 season-opening victory over Arkansas State. Mariota coolly guided Oregon’s speedy spread offense, completing 18 of 22 passes. 

“The game in itself, it was fun,” he said. “I can’t really explain it any more than that.”

Sophomore De’Anthony Thomas caught two of Mariota’s scoring strikes and ran for another touchdown while collecting 119 yards in total offense. 

Kenjon Barner, taking over as starter after the departure of running back LaMichael James, ran for 66 yards and two scores.

Mariota, Thomas and Barner were finished by halftime while Oregon coach Chip Kelly gave his backups some work. 

“I would have liked to play a little bit more, but that’s the competition nature in me,” Mariota said. 

The loss spoiled coach Gus Malzahn’s first game as coach of the Red Wolves, who went 10-3 last season and won the Sun Belt Conference title.   

“We had an idea about their offense. They execute it so well and they’ve got speed at every position,” Malzahn said. “Obviously, we were expecting to do better than we did defensively in the first half.”

Arkansas State senior quarterback Ryan Aplin threw for 304 yards and three touchdowns, including a 72-yard scoring pass to Julian Jones just before the half. 

Mariota replaced Darron Thomas, who decided to leave Oregon with a year of eligibility left. Thomas passed for 2,761 yards and a school-record 33 touchdowns last season when the Ducks went 10-2 and beat Wisconsin in the Rose Bowl. 

Mariota was on the practice squad last season and was something of a mystery because Oregon closes practices, but he beat out Bryan Bennett for the starter’s job in fall camp. 

The native Hawaiian had shown promise in the Ducks’ spring game with a touchdown pass and two scoring runs — including one TD rush of 82 yards. 

Mariota is the first freshman to start in an opener for Oregon since Danny O’Neil in 1991.  

The Ducks scored on their first drive of the game with Barner’s 4-yard dash, then added the 2-point conversion to make it 8-0. 

Barner, a senior, was James’ backup for the past two seasons. James, the school’s career leading rusher, left Oregon early for the NFL draft and was a second-round pick by the San Francisco 49ers.   

Mariota connected with Thomas with a 12-yard pass to make it 15-0. 

Thomas made a splash last season when he set an Oregon freshman record with 18 touchdowns, rushing for seven, nine on receptions and two on kickoff returns.   

Before the first quarter was over, John Huff pulled down a 4-yard touchdown pass from Mariota and Barner added a 17-yard scoring run to make it 29-0. 

Brian Davis kicked a 43-yard field goal for the Red Wolves early in the second quarter.  

Thomas scored twice, once on a 12-yard pass from Mariota and then on a 33-yard run to make it 43-3, and there was still 10:45 left in the half. True freshman Byron Marshall added a 3-yard TD run for the Ducks. 

Aplin passed to Jones, who ran down the right side to close the gap a bit with 3:20 left in the half, before Davis opened the third quarter with a 29-yard field goal.   

Aplin added a 6-yard touchdown pass to Josh Jarboe before the end of the quarter to make it 50-20.    

Bennett, who came in for Oregon in the second half, found Rahsaan Vaughn with a 7-yard scoring pass, before Aplin’s two final touchdowns, a 38-yard pass to Carlos McCants and a 1-yard keeper with 4:30 left.

“We gave up a lot of points,” Barner said. “Whether it was the starters or not, we have to do better than that.”  

Arkansas State and Oregon had never played each other. Indeed, the Red Wolves had never faced a Pac-12 foe. 

“I don’t know if you saw how big they were, they all looked like giants out there,” Aplin said. “We hurt ourselves early, but it was tough.”