LAS VEGAS -- Marcus Mariota, a former Heisman Trophy winner, No. 2 overall NFL draft pick and the highest-paid backup quarterback in the NFL with a base salary of $7.5 million, made his season debut for the Raiders on Thursday night, filling in for an injured Derek Carr in their dramatic 30-27 overtime loss to the Chargers.

Las Vegas has lost four of five and is now 7-7 after a defeat that all but ended its playoff hopes.

Mariota led four scoring drives, but Las Vegas' defense could not keep the Chargers out of the end zone after the Raiders took a 27-24 lead on a field goal with 3 minutes, 18 seconds to go in the extra period.

"It just shows the kind of player, the kind of football character he has," Raiders coach Jon Gruden said of Mariota. "You lose Derek, and then we change gears offensively. And Marcus came in and did a great job. Really proud of him. I think that this kind of puts an exclamation point on why we signed him and just wish we could have won the game for him."

Chargers rookie quarterback Justin Herbert, who idolized Mariota at Oregon, snuck it in from 1 yard out on third-and-goal for the victory with 1:29 remaining to improve the Chargers' record to 5-9.

Mariota, who signed a two-year free-agent contract worth $17.6 million with Las Vegas in March, came in after Carr suffered a groin injury scrambling toward the end zone late in the first quarter.

Gruden didn't have any immediate specifics when asked afterward about the severity of Carr's injury, saying: "I don't believe it's a real tear, but if he can't finish the game, it's got to be pretty significant."

In his first substantive NFL appearance since Oct. 13, 2019, Mariota directed three touchdown drives and showed not only a willingness but an ability to extend plays with his legs as he rushed for a game-high 88 yards on nine carries, including a hard-charging 2-yard touchdown run to tie the score at 24-24 in the fourth quarter. He also passed for 226 yards and a score while completing 17 of 28 attempts with an interception.

"When it comes down to it, it's part of your job -- to be prepared," Mariota said. "It's just fun. It's fun to play. ... I think of myself as a point guard and try to distribute and give our guys an opportunity to just go out there and play. Sometimes the defense is going to give you some scrambling lanes, and I just try to execute and make first downs and keep the rhythm going."

After entering the game, Mariota promptly led the Raiders on an 86-yard scoring drive in seven plays, hitting tight end Darren Waller on a perfectly placed 35-yard touchdown pass down the left sideline to give Las Vegas a short-lived 10-7 lead. It was Mariota's first touchdown pass since Sept. 29, 2019.

Included in that drive was an 11-yard run on a read-option play, a specialty of Mariota's in his career, and a facet of the Raiders offense that has been missing.

"If Derek can't go, we're going to always try to do what our quarterback does best," Gruden said. "This guy can really run, he's a dual threat, and he proved it tonight."

A 76-yard touchdown drive in the third quarter included Mariota keeping the series alive by running for a first down on fourth-and-2. Josh Jacobs' leap over the pile from a yard out tied the score at 17-17.

Bridging the third and fourth quarters, Mariota led the Raiders on a mind-numbing 19-play, 75-yard drive in 10:52 that included a pair of fourth-down conversions and culminated with his 2-yard scramble and touchdown plunge.

It was only the third time Mariota was active this season after being slowed by shoulder, elbow and ankle injuries during training camp.

As noted by ESPN's Field Yates, Mariota stood to make some money in the game. If he plays more than 60% of the snaps in any game this season, he earns a $200,000 incentive. With a victory, that number jumps to $325,000. Plus, by playing in 60% of the snaps in a game, his base salary increases by $625,000 in 2021. He had nearly $1 million to make against the Chargers.

Mariota, the Heisman winner out of Oregon in 2014 and the second overall pick of the 2015 draft by the Tennessee Titans, was supplanted in Nashville last season by Ryan Tannehill.

Mariota said he was impressed by Herbert.

"It was special for me," Mariota said. "I've gotten to know Justin. Him and my brother were close at Oregon, so it was really cool to see his level and how he's playing and how well he's been doing. It was cool to see him [tie the rookie passing TD] record and, again, being a fan of the game, being a fan of Oregon players, it was really cool and really special for me."

Said Herbert: "It was a pretty crazy experience. I grew up watching Marcus. He was my favorite player. To see him on the field and play against him was really cool. It's everything I've ever wanted."

When Carr, the Raiders' franchise all-time passing leader, went out, he had completed 3 of 5 passing attempts for 53 yards.

"This is Derek's team," Mariota said. "For me, I just try to come in and help these guys and try to get a win. Derek is a great leader and somebody that this team can look to. It was cool for me to get to experience playing again, not playing for a while, and to have his support, have Coach Gruden kind of make things that transition real easy for me, meant a lot. And I thought that was the reason we had some success."