The Broncos’ defense has a new problem to repair before Sunday’s game against Pittsburgh. But that has been common this season. Just when one area appears patched, something else breaks. Consider:

Rush defense: During a three-game stretch (Weeks 4-6), the Broncos fell from third against the run to last. But they have held their last five opponents under 100 yards.

Takeaways: They had only two from Weeks 2-6, but have eight in the last four games.

Sacks: The pass rush slumped (five in Weeks 2-6), but they have 20 sacks in the past five games.

The new issue? Third down defense.

In Sunday’s win over the Los Angeles Chargers, the Broncos allowed quarterback Philip Rivers and Co. to convert nine of 15 third down chances (60 percent).

“That was embarrassing, how we played on third downs,” Broncos coach Vance Joseph said. “Honestly, it was embarrassing.”

The success rate was the highest allowed by the Broncos since Carolina in the 2016 opener and the nine conversions were the most allowed since Kansas City had nine in Week 16 of 2016.

The Broncos defense exited their bye week ranked 11th on third down (37.1 percent), but are now tied for 19th (40.0).

The task becomes even more difficult against the Steelers, who are sixth on third down (46.8 percent) and lean on receivers Antonio Brown and JuJu Smith-Schuster and receiving running back James Conner as options.

What made their third down work (or lack of) on Sunday even more frustrating to Joseph is how the Broncos played defensively on first down. The Chargers entered the game averaging a league-leading 7.6 yards on first down. But on Sunday, the Chargers averaged 5.6 yards on 32 first-down snaps, including only 2.6 yards on 16 first-down snaps in the first half.

“Our issues on defense weren’t on first (or) second down, stopping the run or even in the pass game,” Joseph said. “It was really third downs.”

Los Angeles converted third-and-6, -10, -10, -8 and -7 … in the first half. Rivers was 8 of 8 for 176 yards on third downs in the first half.

“All their big plays came on third down, which is rare for our football team,” Joseph said.

Indeed, in the previous four games, the Broncos had allowed only four “explosive” plays (rush of at least 12 yards/pass of at least 16 yards) on third down. The Chargers had six.

So what was the issue?

“It wasn’t the play-calling; we just have to be better,” safety Justin Simmons said.

The Chargers took advantage of man-to-man coverage — seven yards to Keenan Allen against Chris Harris, 14 yards to Antonio Gates against Su’a Cravens, 27 yards to Mike Williams against Harris and 27 yards to Gates against Cravens). And the Chargers should have put the game away with 3:21 remaining when Gates got away from Simmons for 25 yards on third-and-6, giving Los Angeles a new set of downs.

“Sometimes, it was bad eyes,” said Simmons, referring to some of the breakdowns. “What it comes down to, we just didn’t execute.”

“Some execution, some calls — it’s all of us,” Joseph said. “We’ve got to fix that because you can’t be that bad on third down.”

Footnote. The Broncos placed left guard Max Garcia on injured reserve Tuesday and signed Cyrus Kouandjio. Garcia tore his ACL last Thursday in practice. Kouandjio, 25, played in three games for the Broncos last year and was in this year’s training camp, but was cut Sept. 1.He will be a reserve tackle because Elijah Wilkinson and Billy Turner, the reserve tackles to start the year, are now the starters at right and left guard, respectively.