Danny Trevathan, middle, has become a vital member of the Denver Broncos’ defense. (Jamie Squire/Getty Images)

The season started embarrassingly enough, and even so many weeks later, it’s not something Denver Broncos linebacker Danny Trevathan enjoys recalling.

First, the good: During a nationally televised, season-opening game against the Baltimore Ravens, the defending Super Bowl champions, Trevathan stepped in front of a pass from Joe Flacco in the fourth quarter, intercepting it and bolting toward the end zone. Then, this: He ran toward the goal line, an easy touchdown — only, with his mind already on his celebration, the second-year defender flipped the ball from his hand at the 2-yard line.

“I saw those lights and I’m there — I’m going to go ahead, get my little dance in, do whatever,” Trevathan said this week. “That was just the young part of me.”

As his teammates chased the fumble — a scrum in which fellow linebacker Wesley Woodyard was mildly injured — Trevathan danced in the end zone.

“That was fairly embarrassing,” Broncos Coach John Fox said this week. Trevathan can smile now about a play that was replayed again and again, showing a young player’s mental error and revealing to America — in one seven-second clip — a symbol of Denver’s defense, the mighty Broncos’ one weakness.

After Seahawks quarterback Russell Wilson led his team to an NFC championship game win against the San Francisco 49ers on Sunday, the Post Sports Live crew looked at the 2012 draft class and debates whether Wilson, Andrew Luck or Robert Griffin III will win more Super Bowls in their careers. (Post Sports Live/The Washington Post)

That was nearly five months ago, long before Trevathan and the Broncos prevented a New England comeback last Sunday to reach the Super Bowl. Although the wound of Week 1 still feels fresh to Trevathan, the memory motivated the young linebacker, and he lately has become the overlooked face of an overlooked defense.

“It taught me to be a little bit more humble,” he said.

Trevathan was easy to miss in college, his ability buried under two unmistakable disadvantages: Even now, he’s listed at 6 feet 1 and 240 pounds, small by Southeastern Conference standards. He also played at Kentucky, one of the conference’s weakest teams. During the 2012 NFL draft, he fell to the sixth round and played little as a rookie, waiting behind star linebackers Elvis Dumervil and Von Miller.

After Dumervil joined Baltimore, Trevathan stepped into the starting lineup, albeit for a defensive unit overshadowed by quarterback Peyton Manning and one of the league’s most explosive offenses.

The Broncos’ defense would be an afterthought, and through most of the season, it played that way. Denver ranked 27th in pass defense during the regular season, and in four games it allowed at least 440 total yards — including a season-worst 522 in a shootout against the Dallas Cowboys. In that game, Cowboys quarterback Tony Romo passed for a franchise-record 506 yards, but the Broncos clinched the victory after Trevathan’s fourth-quarter interception. This time, he held on.

“We needed this,” Trevathan said after the 51-48 win, and the truth was, he probably needed it, too.

Denver seemed like a Super Bowl contender, sure, but for a long time it seemed like one in spite of its defense, and only if Manning could consistently score enough points. In two of the team’s three losses, the Broncos allowed opponents to build big leads; in the other, more glaring loss, the defense couldn’t protect a 24-0 halftime lead against the Patriots and quarterback Tom Brady.

“Life is a game,” said Trevathan, who had a season-high 13 tackles in November’s overtime, 34-31 loss to New England. “It’s ups and downs, highs and lows.”

Around that time, Trevathan would say later, he noticed himself growing up. The interception-turned-fumble in September had humbled him, and the November birth of his first child, a daughter, matured him.

“She has just helped me get myself together,” the 23-year-old linebacker said.

The Broncos’ defense, though, was another story. Coordinator Jack Del Rio took on interim head coaching duties while Fox recovered from an emergency heart procedure, standing in for the head coach for four games — and keeping the team’s big dreams from derailing. They defeated division rival Kansas City twice during that stretch, protecting Denver’s AFC West lead, and Del Rio leaned on players like Trevathan and his newfound steadiness. Players, meanwhile, strengthened their trust in Del Rio, whose leadership made him a head coaching candidate following his 3-1 stand-in performance.

That was the good. Then, this: Miller, a two-time Pro Bowler with five sacks and 28 quarterback hurries, tore the anterior cruciate ligament in his right knee during a late-December game against Houston. Miller’s season was over, the latest obstacle to threaten the Broncos’ year, and Trevathan was now his team’s best outside linebacker.

“We looked at the games remaining,” Fox said, “knowing that we were going to be in the playoffs — we had clinched a spot — and just really being determined to get better.

“We’ve done that, and we need to continue it.”

During the Broncos’ past four games, three of them without Miller, the defense held opponents to an average of 268.5 yards — 103 yards fewer than its average through 14 regular season games.

This past Sunday, during the AFC championship against the Patriots and Brady — who was 10-4 all-time against Manning and 7-0 against Del Rio’s defenses — the Broncos needed to stop a two-point conversion in the fourth quarter. Brady was building another comeback, and two points would trim Denver’s lead to one possession with a little more than three minutes to play.

Del Rio called a play that seemed to indicate that he’d predicted Brady would pass; instead, Brady handed off to running back Shane Vereen, who ran up the middle and encountered a plugged gap — with Trevathan among the three defenders who stopped Vereen short of the goal line.

A day later, the hum of his team’s 26-16 win still spreading through the Broncos’ Dove Valley training complex, Trevathan stood on a stage and smiled. The season had started one way, humiliating as it was. And now, this.

“I promised myself I would never put my team in a place like that,” he said, looking back on that game in September. “I’ll make up for it; I’ll do whatever I’ve got to do. I promised those who were laughing at me, I’m going to make them suffer.”

Then he continued.

“You know, I like my lows and I like my highs,” Trevathan said. “Because without my lows, I never know what my highs are.”