Bo Nix already had a pair of third-down conversions in the bag during Denver’s opening drive Sunday against Carolina when he dropped back on third-and-5 from the Carolina 28 and found disaster.

The maligned Panthers defense had good coverage and Nix hesitated, then backtracked and got swallowed up for a 13-yard sack.

The play knocked Denver, trailing 7-0, out of field position. And while it was uncharacteristic of Nix to take a sack — this was probably his worst of the season — the third-down failure was nothing new.

The Broncos entered Sunday’s game doing nothing worse offensively than converting on third down. They checked in No. 31 in the NFL at a dismal 26.4% and hadn’t had a game where they finished better than 4 of 11 (Week 7 at New Orleans).

Instead of starting another rough day in that department, though, the first-quarter sack was an anomaly.

For the most part, Nix and Denver shredded Carolina’s defense on third down over the course of a 28-14 win. In fact, the Broncos converted nine of their first 10 on the money down and 11 of 17 overall.

“Third downs are something that we wanted to be better at,” Nix said after the game. “We were better today. A big part of that was a lot of third-and-4s, third-and-3s. Third-and-shorts.”

Nix is exactly right. Of Denver’s 17 third-down snaps, 11 of them required 3 or fewer yards for a conversion. The Broncos converted nine of those. They went 1 of 3 on third-and-8 or longer.

The rookie quarterback, in particular, was terrific in this department against the Panthers, though he had help. Nix was pressured only six times on 40 drop-backs, and only two of those came on third down.

Nix finished 9-of-10 passing for 75 yards and a touchdown on third down. In 13 combined passes or runs, Nix generated a first down seven times and a touchdown twice. He’d have notched another on an 8-yard completion to Courtland Sutton on third-and-7 late in the game, but Sutton fumbled.

So Nix racked up essentially 10 hits in 13 tries.

That’s cooking.

“We hit a few tempo plays. We felt like we had a good third-down plan going in,” head coach Sean Payton said Sunday. “We had some other opportunities and some big-play opportunities on one of the third downs. We have to build on that because what we’ve been is not really sustainable for success.”

The play Payton referenced was a third-and-2 deep shot for rookie Troy Franklin up the left sideline early in the third quarter. Franklin ran by the defender but narrowly missed a rainbow throw from Nix. After seeing the play in film review, Payton chalked it up to a close-but-no-cigar moment.

“I love the throw, I love the route, all of it,” he said, explaining that if Nix always throws to or near the sticks on third down, defenses will feel more confident squatting on routes.

The aggressive throw, then, “didn’t bother me at all; I love it,” Payton said.

“On one side of the field, you have (rookie receiver Devaughn) Vele matched up with a linebacker one-on-one,” he continued. “That’s a pretty difficult scheme. Then on the other side of the field, we have a guy that we feel like we can run by in the safety. Each week we have to be able to stretch the field that way. I think the route was good, throw was good, location. We’re close on it.”

Speaking of Vele, his stat line of three catches for 28 yards won’t jump off the page, but he made two terrific receptions on third downs to move the chains.

The first was a diving catch on a low throw to the sideline on the Broncos’ first touchdown drive. It kept the offense on the field and the field goal unit on the sideline, and it set up another tough third-down grab, this one a touchdown from tight end Nate Adkins.

Vele later made a toe-tap grab for 16 along the sideline to convert another third down.

Pretty much everything went Denver’s way on third down against the Panthers. Of course, Carolina sports the second-worst third-down defense in the NFL and Payton went out of his way to say several times that better teams are ahead.

Still, it’s better to see success and then try to build from it than the other way around.

One small thing I liked >> Sometimes a guy’s hard-wired personality shows through. That was nickel Ja’Quan McMillian after the game Sunday when asked about his impressive, perhaps touchdown-saving interception midway through the fourth quarter.

“It’s been, what seven games and I hadn’t got one yet, so that just took a whole burden off my shoulders,” he said after the game. On Monday, he added it’s the longest stretch he can ever remember playing without a pick.

That tracks with what secondary coach Jim Leonhard told The Post earlier this season. McMillian’s played solid, reliable ball and has been a substantial contributor to Denver’s top-flight defense, but he’s used to making big plays like the run he went on in the middle of the 2023 season.

“That’s his personality,” Leonhard said of McMillian. “You just want him to understand: Don’t force it. You’re playing extremely well. You’re making this defense so much better by what you’re doing right now. Don’t try to force that big play that you’re accustomed to making. They’re going to come. Don’t worry about it.”

One small thing I didn’t like >> The Broncos’ opening defensive drive didn’t go well, and one department in particular stood out. Denver’s been a good tackling team overall this year but struggled early against the Panthers. On their opening 10-play, 49-yard touchdown drive there were at least seven identifiable missed tackles. Some hurt worse than others — three misses against receiver Xavier Legette on an end-around still resulted in no gain — but the tackling was leaky.

On top of that, Miles Sanders pushed the pile a good 5 yards on third-and-3 for a 7-yard gain and Chuba Hubbard went 13 on a screen pass that Denver didn’t do a good job of shutting down.

These are the little things Vance Joseph’s group did better as the game went along. But they’ll sting more against upcoming foes like, for example, Baltimore running back Derrick Henry.

One trend to watch >> Nix spread the ball around Sunday, completing passes to 11 players. That included five wide receivers, three tight ends, two running backs and fullback Mike Burton.

It’s the second time in four weeks Nix has hit 11 receivers in a game. Some of that is by happenstance, but it also suggests Nix is capable of getting through his reads and delivering the ball where it’s supposed to go.