LAS VEGAS — This was supposed to be the year when the Kansas City Chiefs were vulnerable. Their wide receivers were dropping passes, their offense was committing penalties, Travis Kelce was supposedly getting old and there was no way that Andy Reid and Patrick Mahomes could possibly overcome all of that.

Yet they did, and wiped away any doubt that the Chiefs are the new NFL dynasty.

With their come-from-behind overtime win over the San Francisco 49ers in the Super Bowl on Sunday night, the Chiefs raised their third Lombardi Trophy in four trips over a five-year span. And they became the first team since the New England Patriots with Tom Brady two decades ago — the last great football dynasty — to successfully defend their title.

Even Mahomes, when asked whether the Chiefs had become a dynasty, replied: “It’s the start of one.”

“It’s a little bit surreal,” Reid said. “I don’t know what a dynasty is. You guys have the thesaurus, so you can figure it out. It’s a great win because I know how hard it is to do and how hard the season was, the ups and downs of the season, and how proud I am of the guys for just hanging with each other and staying positive with each other.”

Never before has an underdog in back-to-back Super Bowls won both, and that may best illustrate two important facts: The Chiefs were eminently beatable this season, and nobody was able to beat them when it mattered.

Start with the roster, which had to be creatively put together by general manager Brett Veach around $37 million in salary cap space taken up by Mahomes, the biggest cap hit in the NFL this season. Yet the architect of each of their last three title runs was able to find bargains such as Jerick McKinnon and Drue Tranquill who contributed far beyond their monetary value.

Look at their wide receivers, youngsters and journeymen who dropped more passes than any team in the league this season. Yet they galvanized around a quiet rookie, Rashee Rice, who not only became their No. 1 option but a bona fide star.

It goes beyond personnel, though. Consider the road Kansas City had to navigate this season.

At one point, the Chiefs played six consecutive games in which the other team had extra days of rest, the only time that has happened in NFL history. They had to play in Germany, beating the Dolphins in Frankfurt in a preview of a future wild-card game, and at one point lost five of eight midway through the season to drop to the No. 3 seed for the playoffs.

After beating the Dolphins in the fourth-coldest game in NFL history, the Chiefs hit the road in the postseason for the first time in six years with Mahomes as the starter. But as underdogs in Buffalo and Baltimore, the Chiefs embraced their newfound status as hunters rather than the hunted, and they responded by playing their best football of the season.

In terms of strength of opposition, the Chiefs successfully navigated the toughest path to the Super Bowl in history.

Then came a fitting finale in Las Vegas.

The Chiefs started off by making the same silly mistakes that dragged them down too often during the regular season, and they fell behind San Francisco by double digits, just as they did in each of their four Super Bowls with Mahomes under center. But just as they did in beating the 49ers four years ago, and the Eagles last year, the best team of its era rallied around what is fast becoming the best quarterback of any era to mount a comeback to remember.

Mahomes drove the Chiefs for a field goal to tie the game 16-all with about 5½ minutes to go. He drove them for another field goal with 3 seconds left to force overtime. And he answered a field goal by San Francisco to start the extra session with a gutsy drive that Mahomes capped with his winning touchdown throw to the much-maligned Mecole Hardman.

“Same as always,” 49ers coach Kyle Shanahan said of Mahomes afterward. “He’s unbelievable.”

Same as always for the Chiefs: unbelievable.

“They’re all tough. I’m not going to say one’s tougher than the other,” Mahomes said of the championship run. “It takes your best, and I think for me, personally, it was just battling through adversity throughout the season, whenever the offense wasn’t playing like I wanted it to play, and just to believe and fight. But all these games are tough. It takes your best football.”

Reid and Kelce assuaged some concerns among Chiefs fans that they would retire after the Super Bowl, saying late Sunday both planned to be back next season. Mahomes and most of their key players also will be back, though some difficult decisions loom when it comes to pending free agents.

All-Pro defensive tackle Chris Jones and cornerback L’Jarius Sneed will demand massive contracts, and the Chiefs need to be mindful of next year, too, when they have several more important players reaching free agency.

The Chiefs will celebrate their latest Super Bowl triumph with a parade through downtown Kansas City on Wednesday, and after a brief exhale, Veach will join Reid and the rest of their brain trust in getting back to work. The cycle will begin anew.

Because sustained success — the kind the Chiefs have achieved, year after year — is what turns great teams into a dynasty.

“I mean, I’m going to celebrate tonight. I’m going to celebrate at the parade,” Mahomes said after earning his third Super Bowl MVP award, “and then I’m going to do whatever I can to be back in this game next year, and try for that three-peat.

“I think Tom said it best: Once you win that championship, and you have those parades and you get those rings, you’re not the champion anymore,” Mahomes added. “You have to come back with that same mentality, and learn from guys like that that have been the greatest of all time, at the top level, and so that is my mindset. I’m going to celebrate with my guys because of how we’ve done this, but then we’re going to work our way back to this game next year.”