While the pair of true freshman quarterbacks garner most of the much-deserved attention, No. 10 UCLA and No. 19 BYU’s defenses figure to decide Saturday’s critical top 25 matchup at the Rose Bowl.

The Bruins’ Josh Rosen went from the nation’s top-rated high school quarterback a handful of months ago to the starter after winning the job over the summer, and the Cougars’ Tanner Mangum became the starter after Heisman Trophy candidate Taysom Hill went down in the opener against the Nebraska.

All eyes will be affixed on how the young passers adapt to arguably the biggest games of their very early careers, but based on BYU’s performance against the pass, Rosen may have the easier task ahead of him.

The Bruins, despite playing two unranked teams in Virginia and at UNLV, are letting up a mere 9.5 points and 139.5 passing yards per game thus far, further wreaking havoc on opposing passers with three interceptions and two sacks.

Much of that early success stems from an experienced frontline. Juniors Deon Hollins, Myles Jack, and Kenny Clark have played a total of 75 games together, and have accounted for the loss of defensive lineman Eddie Vanderdoes, who went down with a torn ACL in the opener against Virginia and is out for the season.

How Mangum responds to UCLA’s frontline, not to mention the pressure of pulling off a second-straight upset over a ranked opponent that would further propel BYU up the national rankings, will undoubtedly decide the Cougars fate for the rest of the season.

It doesn’t help Mangum’s case that the Cougars defense has let up huge chunks of yardage and points and required late-game heroics from their quarterback to bail them out. BYU’s allowed 52 points and 806 yards through two games, but does deserve heaps of credit for taking down much tougher opponents in Nebraska on the road and then-No. 20 Boise State.

The Cougars starting defensive backs, Micah Hanneman, Kai Nacua, and Michael Davis have been burned for 308 yards per game and four total touchdowns, a group Rosen will try to exploit.

However, BYU has done a tremendous job pressuring opposing passers which could make for another huge upset. Junior linebacker Harvey Langi leads the squad with 3.0 sacks and senior defensive lineman Logan Tael’s tallied 1.5 sacks thus far against strong Cornhusker and Broncos offensive lines.

They’ll be tabbed to break through a Bruins line that has kept Rosen clean and without a sack through two games.

Kickoff Time: 10:30 p.m. ET

TV Channel: Fox Sports 1

Live Stream: Fox Sports Go