For all but a few days each year, Washington’s Chris Petersen and Oregon’s Mark Helfrich will remain close friends.

“The guy’s a lifelong friend of mine and that won’t change,” Helfrich said. “I know that’s going to make both of our fan bases very unhappy.”

Petersen and Helfrich, who met in 1997 as assistants on the Oregon staff, will square off for the first time as head coaches Oct. 18 in Eugene. The rivalry, surely, will remain unfriendly.

Helfrich, in his first matchup against the Huskies last year, rode the right arm (and long legs) of quarterback Marcus Mariota, who had arguably the best game of his career, throwing for 366 yards and three touchdowns and rushing for 88 yards and another score in the Ducks’ 45-24 victory at Husky Stadium.

Ducks fans, no doubt, were happy when Mariota announced he would return to school for the 2014 season, turning down a chance to be the No. 1 overall pick in the NFL draft. Mariota is now a favorite to win the Heisman Trophy, and Oregon was picked as the favorite to win the Pac-12 Conference title this season.

“He’s 100 percent true. He’s 100 percent dedicated to the team. He’s 100 percent credible,” Helfrich said of Mariota. “A lot of guys talk a good game. Everything that guy does is gospel. If I’m the backup guard and I see that guy forgo what he could have made … that’s huge. I think it speaks to the type of guy he is.”

Mariota, a fourth-year junior, said the decision was simple.

“For me, my major focus is to get my degree. That’s why we go to school, to get a degree,” said the 6-foot-4, 219-pound native of Honolulu. “I made a promise to my parents that I’d get it, and that’s ultimately why I came back to school.”

Oregon, ranked No. 2 in the polls in early November, fell out of the national-championship picture in 2013 after Mariota was hobbled by a partial sprain of the MCL in his left knee. The Ducks lost at Stanford and, in a stunning upset two weeks later, lost at Arizona, 42-16. They wound up settling for a berth to the Alamo Bowl, where they beat Texas. The 11-2 finish was a bit of a letdown for a program that had been to four consecutive BCS bowl games.

“Looking back to last year, it’s a great thing for our players to kind of slap ourselves in the face and go back to ‘process,’ go back to ‘culture,’  ” Helfrich said.

With the retirement of longtime defense coordinator Nick Aliotti (he’s now an analyst on the Pac-12 Networks), Helfrich handed the keys to the defense to another longtime assistant, Don Pellum, who inherits two potential first-round picks in cornerback Ifo Ekpre-Olomu and defensive tackle Arik Armstead.

The Oregon offense, second in the nation with 565 yards per game last year, must replace two starters lost to injury: receiver Bralon Addison and left tackle Tyler Johnstone, both to ACL injuries. But the Ducks add intriguing newcomers to their Mach-speed attack: receiver Devon Allen and running back Royce Freeman.

Freeman has been the buzz of fall camp, with the 6-foot-2, 229-pound true freshman emerging as a potential starter at running back.

“I think he is going to be a really, really special guy,” longtime UO running backs coach Gary Campbell told reporters.

Allen, meanwhile, is coming off a really, really special spring in which he won the NCAA track title in the 110-meter hurdles in 13.16 seconds — the second-fastest time in NCAA history.

“Devon Allen will take off his Superman cape from track … and we expect great things from him,” Helfrich said.

Adam Jude: 206-464-2364 or ajude@seattletimes.com. On Twitter @a_jude.