SAN DIEGO -- The Broncos' hopes for a last-second, comeback win hung in the air as a Hail Mary rocketed through the San Diego sky.

And just as quickly as Trevor Siemian unleashed the deep throw from 45 yards out, those hopes came crashing back down.

"We had a lot of self-inflicted wounds," Siemian said. "Those are tough to overcome, and we didn't make the most of our opportunities, I thought, early in the game. We showed a lot of resiliance there at the end, but it was too little, too late for us."

The improbable resurgence from 18 points down in the fourth quarter almost happened. After a lethargic first half, Trevor Siemian and the Broncos almost handed another heart-wrenching loss to the San Diego Chargers. But on a night when the offense seemed like it couldn't get out of its own way, Denver came up just a few yards short after an onside kick recovery gave them a chance.

Siemian evaded defensive linemen, scrambled to his right and hoisted the football into the air, but he couldn't get enough juice on the throw, which was harmlessly knocked to the ground short of the end zone.

"I was kind of upset about that," Siemian said. "I don't even think I got it in the end zone. Probably threw it too soon. It's a shame because you get a chance to tie the game up there at the end and I don't even think I got it in there. That was my fault. I'd like to do that one again."

Not much went right early on in Trevor Siemian's return from injury.

The offense gained just 113 total yards through the third quarter as Siemian went 13-for-23. The Broncos struggled in nearly every category on Thursday as they put together just two drives of more than 20 yards until the fourth quarter. He did put things together late as he led a 51-yard touchdown drive and a 56-yard field goal drive, but the early hole was too much to overcome.

One positive, however, was that Siemian said he "didn't really have any problems with" his non-throwing shoulder that he injured in Week 4 against the Tampa Bay Buccaneers.

Despite the struggles in the first half -- which included an early overthrow that would've been a deep touchdown if completed -- Siemian said he didn't necessarily feel like he had a big turnaround in his play after halftime.

"It didn't feel like that," Siemian said. "I can look back and off the top of my head, I can -- a handful of plays that if you make, you don't know how it turns out, right? I'd like to go back and watch it, but a lot of credit to San Diego. I think they did a good job mixing up looks and they played well all across the board."

Some of the struggles can be attributed to a lack of explosiveness on the outside. The staples of the Broncos' offense, wide receivers Emmanuel Sanders and Demaryius Thomas, were held to just nine catches for 75 yards as Denver failed to stretch the field.

"I think too we got behind a little bit early and the combination of Demaryius and Emmanuel, that might scare some people and they want to keep a lot of things in front of them," Siemian said. "That's just how the game unfolded. I'm sure each team plays it a little different. Again, tough when you're down so much. You kind of play into their favor when you're just dinking the ball down like that. I think we'll get it fixed, though. I feel pretty good about that."

When asked whether the absence of Head Coach Gary Kubiak played a role in the offense's struggles -- which include that very lack of a deep threat -- Siemian said he wasn't sure. Offensive Coordinator Rick Dennison called the plays for the Broncos on Thursday, but it did not affect the relay to Siemian, as Quarterbacks Coach/Passing Game Coordinator Greg Knapp continued to feed him the calls. And with as many duties as a head coach shoulders during a game, Siemian said he's used to limited contact with Kubiak during games.

"It's tough to tell," Siemian said. "You miss him in-between series every now and then. You get a chance to talk to him, but he's got so much going on during the game that for me it's tough to tell how much of a difference that makes. I thought Joe D. did a good job communicating with everybody and really did a good job with the group."

While DeCamillis handled the team well in Kubiak's stead, the Broncos were unable to pull out the division win. And with the loss, they fell from a team that was 4-0 just 10 days ago to one that's 4-2. When asked about the stark and rapid change, Siemian said he knows that's just life in the NFL.

"I think this is a tough league," Siemian said. "And we're playing a tough team. We knew that going in. I think the one thing about this team is the resilience and that was a staple of us last year, as well. All the guys in that locker room, even the whole game, the sense was we were going to figure it out and we were going to get this thing going and make a run at it. Again, it was just too little, too late."