DENVER — For a moment, it appeared the Broncos' offense was going to enjoy a smooth transition between training-camp hype and game-day success.

On first-and-10 from his own 25-yard line, quarterback Case Keenum dropped back and fired a short pass to Demaryius Thomas, who caught it on the right side of the field and scooted up the sideline for 5 yards.

Keenum and the offense, though, wouldn't complete another pass.

When they got back up to the line of scrimmage, right tackle Jared Veldheer was whistled for a false start, and Keenum and the offense couldn't overcome the second-and-10. After a 3-yard run by Devontae Booker, Keenum sailed a pass over Courtland Sutton's head, and the Broncos were forced to punt.

The results were similar on Denver's second drive, as Keenum failed to connect on his second- and third-down passes after an opening run of 4 yards.

"That's kind of the nature of NFL football, especially at this level, especially against a really good defense," Keenum said after the game. "You can't have negative plays, can't have penalties. Those things set you back. We never got into a rhythm. Never got that first, first down or got going. Definitely left me wanting more, and I'm sure it's how a lot of people felt."

Head Coach Vance Joseph also chalked the early struggles up to self-inflicted wounds, and while Keenum said he would always prefer to keep playing, he respected Joseph's decision to keep the starters out of harm's way.

That's when Keenum and the rest of the starting offense may have produced the most positive outcome of the evening.

"Training camp and preseason, it's about building a foundation," Keenum said. "It's about finding what you're good at and maybe finding what you're not good at and working on that. We obviously have some things to work on. I think it's a good test for us, going against a really good team that we know is a really good team. We know we've got to work, we've got to get better, hands down.

"I think all of those guys are hungry. Sitting there on the sideline talking to those guys after we were out, every single one of them wanted more. They're ready to go to work this week."

As Keenum and the starters talked on the sideline, second-string quarterback Paxton Lynch encountered some problems of his own. The former first-round pick finished 6-of-11 for 24 yards, no touchdowns and an interception. He was also sacked once as he compiled a quarterback rating of 22.2.

"We didn't really put a lot of drives together and move the ball, so I'm sad about that," Lynch said. "We didn't score a lot of points, but I'll watch the film tomorrow. We'll move on from that and work on Chicago."

Joseph said his evaluation of the quarterback's night won't be complete until after he watches the game film.

"[He was] up and down," Joseph said. "He made some plays, he didn't make some. Up and down. I haven't watched him yet, so I couldn't tell you exactly what I saw. But up and down."

Lynch, who said he did feel like he's taking steps in the right direction as a quarterback, already knows there's plenty of room for improvement.

That, he said, won't ever change.

"There's always things to work on, obviously," Lynch said. "You can go out there and throw four touchdowns and 300 yards and there's still things to work on."

When third-string quarterback Chad Kelly took the field with 6:01 to play and his team trailing by seven points, he seemed capable of delivering a stat line that at least rivaled Lynch's hypothetical performance.

Kelly had already led a pair of touchdown drives that spanned 160 total yards and took the Broncos from a 13-point deficit to a 1-point lead.

"I was looking forward to throwing touchdowns and getting hit and making plays, doing whatever it takes to get my team in the end zone," Kelly said. "It was a decent first game, and I'm blessed to be in [this] situation with a great franchise."

Kelly's third drive didn't end as successfully. On the second play of the drive, Kelly forced a throw toward Jordan Leslie that was picked off by Vikings safety Jack Tocho, and the Vikings added another touchdown on the ensuing drive.

Kelly would flash one more time on the night as he led the Broncos from their 25-yard line to the Minnesota 1-yard line, but time expired as the Broncos attempted one final fourth-down pass.

"He played well tonight," Joseph said. "Outside of the one interception, which led to a score for those guys. He is a guy that plays with a lot of confidence. That's a good deal."

Kelly's play left the Broncos Stadium at Mile High crowd chanting his name, but Joseph wasn't ready on Saturday night to say Kelly had earned second-team snaps for next week's game against Chicago.

"We'll see," Joseph said. "We'll watch the tape and see where we are. Obviously Case is the starter, so that's my main concern."

In his starting role, Keenum found plenty to improve upon — and that was true for the other two quarterbacks on the roster.

As Keenum said Saturday, the preseason opener was just a foundation.

The building process continues on.