COSTA MESA, Calif. -- Los Angeles Chargers wide receiver Keenan Allen walked into the "zoom" room to do his stint with the media, wearing a protective face mask that read, "You've got a friend in me." It was somehow fitting that a rookie he had taken under his wing needed one right then.

Running back Joshua Kelley, rarely seen without a smile on his face, was hurting. Not physically -- that would be another RB in Austin Ekeler ... more about him later -- but emotionally. He had his second straight game with a lost fumble, which, if it didn't cost the team the game against the Tampa Bay Buccaneers, certainly cost the Chargers momentum in a season where momentum had been hard to come by and even harder to keep.

"He's pretty upset right now," said Chargers head coach Anthony Lynn on Monday. "I know his background. I know his life. I know he'll put this behind him, bounce back because we don't have anybody else."

Ekeler, an emerging star and the Chargers' starter, planted awkwardly at the end of a carry with 1:37 left in the first quarter on Sunday in Tampa and was in such agony he had to be helped to a cart to take him off the field, resulting in an injury that will sideline him for at least the next month. It provided a huge opportunity for Kelley, who, like many, had dreamed of playing in the NFL. He didn't want it coming in this way, but 'next man up' has been many a team's motto.

And Kelley had vowed that a game-changing fumble would never happen again after he turned it over in Week 3 against Carolina after a 16-yard run to the Panthers' 43-yard line. Carolina scored eight plays later, helping the Chargers lose a game they were expected to win.

"I go to sleep at night like, 'Dang, man, how differently had the game gone if I had just been more decisive in the open field,'" Kelley said last week.

This time, against Tom Brady and company, it was a botched handoff from another rookie, quarterback Justin Herbert, which the Bucs recovered at the Chargers' 8-yard line. It came with the Chargers comfortably up 24-7 and led to a Bucs' touchdown just before halftime, helping spark a second-half Tampa Bay comeback.

"That play right before the half scared me a lot," Lynn said. "I knew Tampa had some momentum and it showed in the third quarter."

But Lynn is not without compassion for the 22-year-old, who was drafted in the fourth round last spring out of UCLA and has rushed for 174 yards and a touchdown on 52 carries.

"Any time the ball is on the ground like that, it's not one person's fault. It takes two to hand it off," he said. "It can't happen. It's a routine play that we work on every day. It's just unfortunate."

Enter Allen, who Kelley reveres to the point that he says he "takes notes" on what Allen tells him.

"He is one of the greatest receivers ever," Kelley said. "You obviously look up to a guy like that ... try to mimic greatness, and that's what he is."

"(I told him) keep your head up," Allen said this week. "With Ek out we definitely gonna ride you all the way. You got to keep the ball. Every time he gets in the huddle you know, just protect the ball."

For Kelley, the biggest issue won't be remembering to protect the ball, but to forget how he had dropped it. It's easier said than done.

"You've got to be able to leave things in the past and learn from those mistakes and not do it again," Lynn said.

Kelley has to do that quickly. The New Orleans Saints' defense will no doubt be keying on him Monday night, trying to force another mistake.

We don't know if he's sleeping with a ball or putting stickem on his hands, or any of the other sappy "don't fumble" tricks we see in movies. But Kelley has a deep, booming voice, a vivid imagination and an attitude so positive they used to make fun of him for it in college.

When UCLA coaches would yell at him, he'd just smile through the litany of mistakes he was being called out for and move on. Kelley fumbled just three times in two seasons with the Bruins, losing zero.

"(The NFL) is fast. It's really fast," Kelley said of the difference. "We've played some really good teams. We've played some playoff teams. So I got a chance to get a little feel for it.

"You've got to be consistent no matter what."

That's the main point Allen tries to impress on the rookie during their consultations -- that and overall good vibes.

"[Kelley] is one of the guys who gets the ball a lot," Allen says. "So I try to get him positive energy."

Kelley is nothing but confident that he can come through.

"I've learned a lot," he said.