Eugene, OR (SportsNetwork.com) - The annual Civil War is on tap for Friday night, as longtime rivals Oregon State and 12th-ranked Oregon close out the regular season in a Pac-12 Conference showdown.

Oregon State ran out to a 6-1 start to the season and in the process became bowl eligible for the second straight year and for the seventh time in coach Mike Riley's 11-year tenure. Since that fast start, however, the Beavers have been spiraling out of control with four straight loses, including their most recent embarrassing defeat at home to Washington, 69-27.

"It's really, really disappointing," coach Riley said. "We obviously failed in every way."

Oregon was once a national championship hopeful, as it ended October with a perfect 8-0 record and was position at No. 2 in the BCS Standings, but their BCS dreams have been shattered in recent weeks with a Nov. 7 loss to Stanford (26-20), and a Nov. 23 setback at Arizona (42-16), giving the Ducks just their second two-loss season since 2010.

"It's a punch in the gut, no question about that," Oregon coach Mark Helfrich said. "We just have to coach them better, coach them harder. I have to figure out exactly which levers to pull and which buttons to push."

These two teams have met 116 times before, with Oregon holding a 60-46-10 series advantage. The Ducks have a five-game win streak in the series, which includes a 48-24 triumph last season in Corvallis.

Oregon State's offense has posted impressive numbers on the season (34.5 ppg, 461.1 ypg), but the unit has been on the decline in recent weeks, averaging only 17.5 points each time out during its four-game losing streak.

Once a darkhorse Heisman Trophy candidate, Sean Mannion has fallen out of favor in recent weeks. He is still in the midst of an outstanding junior season, however, completing 66.3 percent of his passes for an FBS-leading 4,089 yards with 34 touchdowns and 13 interceptions.

Mannion has displayed great chemistry with Brandin Cooks, who has been setting records left and right. He leads the country in both receptions (110) and receiving yards (1,560), while scoring 15 touchdowns, all of which are single- season school records. He needs just nine more receptions to break the Pac-12 single-season mark.

"(He's) unbelievable. Talent, effort, leadership, all of that," Riley said of his star receiver. "He is just a wonderful kid to have around and he just continues to, I think, be a great example for never quitting. He is shattering all the records right now so it's pretty amazing."

Richard Mullaney (48 receptions, 729 yards, three TDs) sees plenty of one-on- one opportunities with defenses keying on Cooks.

The ground game lags way behind the aerial attack, as its ranks 120th in the nation with just 72.8 yards per game. Terron Ward (322 yards, four TDs) and Storm Woods (297 yards, four TDs) have split carries to minimal effect.

Defensively, Oregon State has disappointed, as it yields 31.7 points per game, although its interception total (17) is tied for ninth-best in the country.

Steven Nelson and Rashaad Reynolds both have five interceptions apiece to lead the ball-hawking unit. Tyrequek Zimmerman has a team-best 84 tackles, while Scott Crichton anchors the defensive line with 14.0 TFL, 6.5 sacks and two forced fumbles.

The Ducks' offense has been a high-flying unit all season long, as they rank fourth in the nation in scoring (47.7 ppg) and third in yardage (573.5 ypg), but they had their worst outing of the year in the 16-point effort against Arizona.

Much like Oregon's national championship hopes, Marcus Mariota's Heisman chances were most likely destroyed by a two-interception performance last week, his only two picks of the season.

"This offense is very rhythm-based, and if you can't get the ball down the field you put a lot of strain on your defense," Mariota said. "Sometimes when you miss those opportunities, you don't get in a rhythm."

The lackluster effort against Arizona hasn't completely dampened an outstanding season for Mariota, who has completed 64.4 percent of his passes for 3,127 yards, run for 529 yards, and accounted for 36 total touchdowns. His passing success has led to big seasons for both Bralon Addison (53 receptions, 798 yards, seven TDs) and Josh Huff (48 receptions, 850 yards, eight TDs) at receiver.

The rushing attack has been outstanding as well. Byron Marshall earns the most work out of the backfield and has turned 155 carries into 995 yards and 14 touchdowns. Thomas Tyner (549 yards, eight TDs) has also been strong, and De'Anthony Thomas (493 yards, seven TDs) is explosive when not hampered by a lingering ankle injury.

Last week's breakdown not withstanding, Oregon's defense has played very well this season, as it allows just 20.4 points and 366.4 yards per game while creating 24 turnovers.

Derrick Malone has a team-best 97 tackles, while Ifo Ekpre-Olomu (66 tackles, two INTs) is one of the best cover corners in the nation. Tony Washington (11.0 TFL, 7.5 sacks, four FF) and Terrance Mitchell (five INTs) are also in the midst of solid campaigns.