Josh Heupel’s No. 6 Tennessee looked like a contender on Saturday night as they rolled to a 25-15 win over No. 15 Oklahoma in the Sooners’ SEC debut. The Vols’ dominant defense forced a safety and rattled Sooners quarterback Jackson Arnold so badly that he was taken off the field late in the first half and replaced by freshman Michael Hawkins Jr. It was a nice homecoming for Heupel, who led Oklahoma to the national championship as quarterback and was later fired as offensive coordinator.

Oklahoma, meanwhile, is battling major injuries, finding its way in the SEC – and has a new problem at quarterback. It was Hawkins who kept Oklahoma in the fight in the second half.

Here are some takeaways from Tennessee’s win.

Heupel has a challenger – that’s better than compensation

The Tennessee coach’s story in Oklahoma has been a big topic of conversation this week. Heupel’s return was triumphant and no doubt a priority for his players. More importantly, this win puts Tennessee in a strong position early for the College Football Playoff. There are two gigantic games left on UT’s schedule, Alabama and Georgia. The Vols will be considered clear favorites to win all other remaining games. It looks like they should be one of the 12 teams in the field. If things continue like this, it could be a lot more. — Joe Rexrode

Arnold out, Hawkins in

Oklahoma’s surprise quarterback change changes the outlook for the season. After a backwards pass bounced in front of a receiver and caused Arnold’s third turnover of the first half, Oklahoma benched him and replaced him with Hawkins. Arnold (7 of 16 passes for 54 yards, 1 interception) did not return until late in the fourth quarter and scored a touchdown.

Hawkins gave OU a boost. A scramble on his second play ended a streak of 10 consecutive plays that ended in a loss or no gain, including two fumbles and a safety, and Tennessee put the Sooners behind 19-3 at halftime.

After Dillon Gabriel threw for 30 touchdowns and 3,660 passing yards but was cautiously sent to Oregon to make room for Arnold, the five-star redshirt freshman prospect, coach Brent Venables’ Sooners face a difficult quarterback problem. This season, Arnold ranks just 73rd nationally in the passer rating and has been responsible for five turnovers in fewer than four games. Hawkins led the Sooners to their first touchdown drive of the night in the fourth quarter, the first touchdown allowed by Tennessee’s defense this season. He completed 11 of 18 passes for 132 yards and a touchdown. What that means for this season and the rest of Arnold’s career remains to be seen. — David Ubben

The Vols play a championship-level defense, especially on offense

Oklahoma’s offensive ineffectiveness in the second quarter of this game may one day be studied and worth reviewing. First possession: run for 0, two incomplete passes. Second possession: run for a loss of 1 and a lost fumble, the play after a UT fumble. Third possession: false start, run for a loss of 2 yards and a UT safety. Fourth possession: pass completed for a loss of 2, two incomplete passes. Fifth possession: pass under pressure that’s a lateral and a lost fumble, the play after a UT fumble. So that’s zero positive plays, two turnovers and a safety, minus 20 yards and the game essentially lost.

Oklahoma finally passed the 100-yard mark with 11 minutes left. At some point, the Vols will encounter a capable passing attack – they haven’t seen one in four games. But UT is well-positioned and well-connected up front, and that can put any offense under pressure. — Rexrode

Sooners plagued by injuries

Oklahoma entered Saturday’s top-15 matchup with injury issues and suffered even more. Receiver Nic Anderson, who caught 10 touchdowns last season, made his season debut but was subbed out after just three snaps and returned to the sidelines in civilian clothes before halftime. The Sooners were already without Jalil Farooq, so Oklahoma had to play without two of its top three targets against a Tennessee defense that entered the game ranked fifth nationally in passing yards allowed per game. Senior defensive back Kendel Dolby suffered a serious lower leg injury and had to be carried off the field. The offense struggled against a fearsome Tennessee front, managing just three points in the first three quarters. — Ubben

Nico Iamaleava overcomes gaps in protection and problems with ball security

The Vols were missing injured left tackle Lance Heard at times, most notably on two strip sacks by Iamaleava. Ball security is the only criticism of Iamaleava on an otherwise encouraging night. In his first chance in a hostile environment, against a defense as legit as Oklahoma’s offense, Iamaleava was composed and precise. He didn’t force any passes, but he made timely throws, including a beautiful pass to Dont’e Thornton Jr., who scored a 66-yard touchdown on the run. His arm was used for just over a half, and he finished 13 of 21 passing for 194 yards. — Rexrode

(Photo of Tennessee defensive lineman Omarr Norman-Lott and Oklahoma quarterback Jackson Arnold: Kevin Jairaj / Imagn Images)