NASHVILLE, Tenn. -- The Indianapolis Colts arrived at their new training camp north of the city nearly 160 days ago with questions about their team.

Could Andrew Luck return to pre-injury form?

How would four first-timers at head coach and the three coordinator positions do in their roles?

That was just the start of their issues.

The Colts fell to 1-5 and looked like they were on their way to another top-10 draft pick after losing to the lowly Jets in October. But through it all, the coaching staff, led by head coach Frank Reich, the players, even the front office never wavered.

Now, 10 weeks after that loss, the Colts are heading back to the playoffs for the first time in four years after winning their biggest game since reaching the AFC Championship Game in 2014, winning 33-17 against the Tennessee Titans on Sunday to clinch the final playoff spot in the NFL.

The Colts will play in Houston against their AFC South counterpart Saturday (4:35 p.m. ET, ESPN). The teams split their regular-season meetings, with each winning on the road. Indianapolis joins Kansas City (2015) and Cincinnati (1970) as the only teams to make the playoffs after starting the season 1-5.

"At the end of the day, what we did is a pretty good feeling," coach Frank Reich said. "To be 1-5 and do something that only two teams in the history of this league ... to make the playoffs after a 1-5 start is quite an accomplishment. Real credit to the guys, and we talked about there's three things. There's trust, there's toughness and there's team, and that's what the foundation is. That's what the culture is. That's what the belief is, those aren't just words. We lived that this year."

The road to the playoffs hasn't been an easy one for the Colts. They faced -- and defeated -- teams on winning streaks of nine, five and four games over the past four weeks to close the season. Indianapolis won nine of its final 10.

The Colts (10-6) didn't talk about it publicly, but knew that expectations weren't high at the start of the season. But Reich, who is known for his comeback heroics as a player in college and during his 13-year NFL career, had his first as a head coach in proving doubters wrong about the season despite having one of the youngest rosters in the NFL.

"I never thought of it as a rebuild," Reich said. "We don't want to hear everything about what everybody said about the roster. We were ranked in all preseason polls. We talked about that, and then we were ranked 32nd after the draft with the draft we had. I like where we're at."

Tennessee entered Sunday on a four-game winning streak, but it had to play to its biggest game of the season without quarterback Marcus Mariota (stinger), defensive lineman Jurrell Casey (knee) and linebacker Brian Orakpo (elbow).

The Colts jumped out to 14-0 lead before several of the "self-inflicted" wounds they always say they need to avoid -- an interception returned for a touchdown, two penalties that negated touchdowns, a fumble lost in Tennessee territory and an unsportsmanlike-conduct penalty that allowed the Titans get within seven points right before halftime -- kept the game interesting. The Colts made it a two-score game and basically sealed their playoff spot when cornerback Kenny Moore intercepted quarterback Blaine Gabbert in Titans territory and Adam Vinatieri made a 25-yard field goal to make it 27-17 with 3 minutes, 55 seconds to play.

It's probably only fitting that Luck led the Colts back to the playoffs on the same field where his climb up the NFL hierarchy ladder at quarterback came to a momentarily halt more than three years ago. In Week 3 of the 2015 season, Luck suffered the right shoulder injury that hampered him for more than two years and forced him to miss all of the 2017 season.

In Luck's first healthy game back at Nissan Stadium, he was 24-of-35 for 285 yards yards with three touchdowns and an interception as he improved his record to 11-0 against the Titans. Luck's 39 touchdown passes were not only the second-most in the league this season, but also the most in NFL history for a player who did not see action in the previous season, according to Elias Sports Bureau research.

"I'm so thankful that I am in good health," Luck said. "That I get to play the game I love with an amazing group of men. So thankful, certainly. Fulfilled in a sense. This really has been a fulfilling road to this point. I'm not satisfied. We certainly have business to take care of."

But this season and the future are longer about just Luck. He's clearly the centerpiece of the offense, but general manager Chris Ballard made sure to point out during his introductory news conference nearly two years ago that the Colts are not just Andrew Luck. Ballard wanted a complete team.

That's what the Colts have this season.

The offensive line -- yes, the offensive line -- tied for first in the league by allowing just 18 sacks this season. Running back Marlon Mack topped the 100-yard rushing mark four times, which is the first time that has happened for the Colts since Joseph Addai did it back in 2007.

"To start protecting the passer, that was a huge focus," Reich said. "And I talked about getting it up front, having an offensive system and plans that would be conducive to protecting the quarterback. The best way is to run the football well. We've been able to do that. Andrew has complete mastery over it. So to protect him the way that we have all year is really satisfying."

The defense, led by rookie Pro Bowl snub and league-leading tackler Darius Leonard, ended the season near the top 10 in the league and didn't give up 100 yards rushing to any player this season despite facing the likes of Adrian Peterson, Ezekiel Elliott and Saquon Barkley. Coordinator Matt Eberflus' ball-hawking style of defense produced a turnover in all but one game this season.

And now the Colts are headed back to the playoffs with their most complete team in Luck's career.

"That's what hard work looks like," Colts defensive lineman Denico Autry said. "We're not done yet."