Niners defensive coordinator Jim O’Neil doesn’t have much reason to smile, but one topic inspired him to flash his pearly whites this week.

When asked about not needing to take rookie defensive tackle DeForest Buckner off the field, O’Neil beamed.

“It’s awesome, isn’t it?” O’Neil said. “It’s so awesome.”

Buckner’s stamina has been awe-inspiring.

Despite missing one game with a foot injury, his 823 snaps are the most of any NFL interior defensive lineman and 38 more than runner-up, Miami’s Ndamukong Suh, according to Pro Football Focus. The Giants’ Olivier Vernon (876) is the only defensive lineman who has played more snaps than Buckner, who has been on the field for 98.3 percent of the 49ers’ plays over the past five games.

In Sunday’s overtime loss to the Jets, Buckner, 22, was out there for all 84 defensive plays — 40 more than any other defensive lineman on the team. It’s the type of iron-man performance that prompted this question: Do you ever feel like collapsing?

“Yeah, I get tired sometimes,” Buckner said. “But I’ve just got to push through it.”

The No. 7 overall pick hasn’t just been indefatigable, he increasingly has been unblockable.

His five sacks rank fifth among rookies, and have all come in his past eight games. He had his second two-sack performance against the Jets, joining fellow top-10 picks Joey Bosa (San Diego) and Leonard Floyd (Chicago) as the only rookies with two multisack games this season. Buckner shares team-high sack honors with outside linebacker Ahmad Brooks, and his 65 tackles rank fourth.

There haven’t been many bright spots in a 1-12 season that has spotlighted many of general manager Trent Baalke’s draft whiffs. But it appears safe to say the bust label won’t be applied to Buckner, whose never-leave-the-field role is partly a nod to injuries along the defensive front.

“He’s probably had to get into that role a little bit sooner than we anticipated, but he’s done a great job,” O’Neil said. “He’s making some big-time plays for us right now, and that’s what you want when you draft a guy seven overall.”

Head coach Chip Kelly, who recruited Buckner to Oregon, said his stamina is a reflection of the “training” he had in college.

However, it’s also a reflection of Buckner’s freakish natural gifts.

At 6-foot-7, Buckner was the tallest defensive lineman at this year’s combine. In addition, his hands — measured pinkie to thumb — are 113/4 inches wide, the largest at the combine since the measurement was first tracked in 2003. At Oregon, he played in 53 of 54 games and his snap total (951) as a senior ranked second among defensive linemen in his draft class.

His block-of-granite status was enhanced when he was carted off the field with a foot injury during a Week 4 loss to Dallas that left him in a walking boot. Despite the apparent severity of the injury, he missed one game and played with discomfort when he returned.

“It sucked getting hurt, and I thought it was going to be more serious than it was,” Buckner said. “But that week that I got off, I just made the most of it in getting healthy and getting back out there.”

The 49ers, who are on pace to allow the most points and yards in franchise history, don’t have a huge core of particularly productive young players around which to build.

One reason to smile: The defensive lineman who doesn’t leave the field isn’t going anywhere.

“At Oregon, the coaches had me going around 80-90 plays a game my senior year,” Buckner said. “So I’m used to it from that aspect, but the NFL is a whole different mind-set. The guys are bigger, stronger. So I’m getting used to that, too.”

Eric Branch is a San Francisco Chronicle staff writer. Email: ebranch@sfchronicle.com Twitter: @Eric_Branch