DETROIT -- Darius Slay was already out. Quandre Diggs was shuffling off to the locker room, not to return. The Detroit Lions’ best cornerback and best safety were out of the game, and the club still had more than a half left of dealing with Kansas City Chiefs quarterback Patrick Mahomes, the strong-armed 2018 Most Valuable Player, trying to dissect their defense.

It would have made sense to think the Lions might have struggled. That Mahomes might have started to pile up yardage. Or throw five touchdowns. Or both.

Except none of that happened. Instead, the Lions held Mahomes without a touchdown for only the fourth time in his career. They held him to his lowest completion percentage in a regular-season game -- at 57.14% -- since Week 1 of 2018. Yes, he threw for 315 yards, but that was also 59 fewer yards than any other regular-season game for him in 2019.

And they did it with a second-year player, Mike Ford, starting at cornerback in place of Slay, and a rookie third-round pick, Will Harris, partially filling in at safety for Diggs.

“Those guys are tough. Those guys are stepping up, man,” linebacker Devon Kennard said. “They faced some injuries and it didn’t seem like they skipped a beat, still played well. So I’m proud of those guys.”

If Detroit can take a moral victory from Sunday's 34-30 defeat, it is that the secondary is something to build on. The expectation is that both Slay and Diggs will eventually return to the lineup, meaning Ford and Harris now have meaningful snaps to build off. And it gives the club even more confidence in what it has, in terms of both starters and depth, at a spot that can be game-changing as the season goes on.

It also should give Detroit even more confidence it has a secondary it can rely on. The Lions won’t face a Mahomesian quarterback every week. They have to deal with Aaron Rodgers twice in their division, but Chicago’s quarterback situation -- be it Mitchell Trubisky or Chase Daniel -- is uncertain. Minnesota's Kirk Cousins has struggled throughout the season.

“I view today that we showed a lot as a team, being able to show that we’re tough, that we don’t give up,” Ford said. “That’s something we pride ourselves in. We have a lot of talent, playing up against that great team. It just shows we’re capable of a lot, so we just have to keep our heads in the right place.”

That shouldn’t be much of an issue once Diggs and Slay return. They learned from one of the better mentors in the game, the retired Glover Quin, and took many football lessons from him as they turned this secondary into their own.

Add in that Justin Coleman, whom the team signed as a free agent this summer to become a strong nickel corner, has consistently played well -- including four tackles, two passes defended, one forced fumble and one fumble recovery against Kansas City.

He’s become a valuable option against the slot and showed -- when Ford left the game briefly due to injury -- he can play on the outside as well. Detroit might not have all of its secondary pieces yet. The Lions might still be figuring all of that out. But when they do, they’ve shown enough to believe they can be a problem for almost any quarterback.

“We knew they were going to double [Travis Kelce] a lot,” Mahomes said. “We knew they were going to play some man coverage. They just did a good job of it.”

So yes, Detroit was disappointed it didn’t win Sunday. It should be -- the Lions played well enough to have won. But there’s also a lot to build on, and much of that starts with the beaten-up group at the back that played without its two best players and still managed to make a difference.

“I feel like we can compete with the best of them and obviously that just showed. Kansas City is a great team, the best team in the league so they say,” safety Tracy Walker said. “They have a great squad over there and we fought them teeth in and teeth out.

“All we can do now is look at the mistakes we made, take the good with the bad and move on. We got to prepare for Green Bay.”