SAN FRANCISCO -- It's one thing to seize attention on the practice field. It's another to do in a game -- even one in the preseason.

That was the test for a slew of young Broncos in the preseason opener Thursday. One by one, they had their chances, beginning with Duke Ihenacho and Julius Thomas in the starting lineup, and progressing to others -- including Brock Osweiler and C.J. Anderson -- as the 10-6 win over the 49ers plowed through the twilight and into the night.

Not everyone on the roster proved worthy, at least not yet. There's three other games, and for most Broncos trying to make their names matter on this level, there's three more chances.

But that quartet made a collective statement that will reverberate through practices and film-study sessions to come: that they won't wilt simply because the stadium lights go on.

It started on the third play from scrimmage when Ihenacho plugged a gaping hole, preventing 49ers running back LaMichael James from ripping off a lengthy jaunt through a defense on its heels. He settled for a 5-yard-gain after being slammed to the earth by the young safety. It was just the beginning; Ihenacho had six more tackles and a forced fumble.

It continued on the first play of the offense's subsequent possession, when Peyton Manning looked to his left and found Thomas open for a 6-yard gain. Forced into extensive service because of injuries to fellow tight ends Jacob Tamme and Joel Dreessen, Thomas led all Broncos in receptions (4), yardage (35), and delivered a key block on the Broncos' longest gain from scrimmage.

"Julius was a stud tonight," Osweiler said.

After a defensive three-and-out in which Ihenacho -- who else? -- had tackles on two of three snaps, Osweiler entered, wasting little time moving the offense into the no huddle. His first drive wouldn't be successful; after an 11-yard completion to Andre Caldwell, a Manny Ramirez holding penalty knocked the offense back 10 yards, and it never recovered. But Osweiler would hold his ground against a daunting pass rush that poured through on play after play, and while he never made the big play, he avoided the mistake that would have provided the 49ers a big play of their own.

And eventually, the line that leaked red jerseys filled its gaps. Osweiler had another second to process the defense and throw. It throttled forward instead of standing flat-footed off the snap. That cleared the way for Anderson, who broke outside of left tackle Paul Cornick and inside a block from Thomas and sprinted 17 yards for the longest gain of the night.

Blocking has been a question mark that hovered around Thomas; it is the most difficult aspect of his long-term transition from basketball to football, and the block to spring Anderson might have been his most gratifying play of the night.

"I just don't want to be one-dimensional, so when I get a chance to help our running backs make big plays, that's something that will make you feel good going back to the huddle. I mean, we were struggling for a little while there, and we got that drive going because of C.J.'s big running. If I can be the guy that they run behind, I'll take it every day."

Ihenacho, Thomas, Osweiler and Anderson were the Broncos' leaders in tackles, receiving yardage, passing yardage and rushing yardage, respectively. No four names were more prominent on the Broncos' stat sheet.

But what does it mean, and how much will it matter beyond Thursday night? That depends what happens from here. One solid preseason performance can snatch attention and validate a series of splendid practices. A stumble next week, and what happened Thursday will no longer resonate.

"I think I had a good game today, but I think it's more about continuously sustaining it," Thomas said. "It can't be an on-one-week, off-one-week thing. I've got to approach next week the way I approached the first week of training camp and continue to do this throughout preseason and into the season."

Thomas can breathe a bit; his position group will be compromised by injury for at least the next three weeks while Dreessen recovers from a second knee surgery in three months. Ihenacho doesn't have the same luxury; most of the Broncos' safeties are healthy, and among the safeties in the mix are last year's starter (Mike Adams), a starter in the 2011 playoffs (David Bruton), and a starter through most of 2011 who has battled knee problems the last 13 months (Quinton Carter) -- not to mention ex-Chargers cornerback Quentin Jammer, who is trying to make the late-career transition to safety.

Ihenacho looked like a worthy first-teamer Thursday. His instincts were as sure against the 49ers as they were on the practice field; he charged forward and diagnosed plays before they developed. He stuffed runs; he excelled against the pass, forcing a fumble that Rahim Moore recovered.

"I see him do it every day in practice, so it's not a surprise to me," said cornerback Champ Bailey. "I know it's going to be a surprise to a lot of people; he hasn't played a lot in this league. But he's coming on. He's a guy that's grown a lot, and he knows how to play the safety position, and I look forward to seeing him play all year."

Ihenacho might have that chance regardless of the health of other players; safety is that wide open, and he appears just that good. That isn't the case for Osweiler and Anderson; they are more likely to be bit players in the Broncos' 2013 opera, and all they can do is perform and be ready in case of injuries.

Ihenacho and Thomas appear closer to their destination; Osweiler and Anderson are knee-deep in the process of developing. That means taking a critical look at each snap and searching for faults, even when none appear obvious.

"There's definitely a couple of plays that stick out in my head that I could have done better at, where I could have made a better play for our football team and for our offense," Osweiler said. "Those are the most important things, that I recognize the plays that were maybe negative, that should have been positive, clean those up, and as long as I can do that, the offense can move down the field."

Three sacks, even under heavy duress, reveal room for improvement. But he was less apt to take off and run with the football, or to dither hesitantly in the pocket. When Osweiler made his decisions, he did so at full speed.

And as Anderson, Ihenacho and Thomas demonstrated, moving at full speed, and making plays while doing so, is the best way to get attention, whether it's at Candlestick Point in front of hundreds of thousands watching on television or when nearly all the cameras are off during a camp practice at Dove Valley.

Together, this quartet showed that this first moment wasn't too big for them. What they do next determines whether larger moments are in their long-term future.