INDIANAPOLIS - When Julian Blackmon went down with a shoulder injury in the first quarter against the Falcons, it was an easy call for the Colts to sub Nick Cross into his spot and keep everything else the same.

When it turned out his season was over, it became time for some reflection.

The staff had some long meetings early in the week in order to find a plan on the back end of the defense ahead of a pivotal matchup with the Raiders. At that point, they did not know that nickel cornerback Kenny Moore II would also end up missing the game with a back injury.

But they felt the need for an experienced communicator with the massive void that came in losing Blackmon. They looked around the roster, and one player stood out.

That was Ronnie Harrison, whom they converted to linebacker in training camp after he spent his first five seasons as a strong safety with 46 starts with the Browns and Jaguars.

"We were going to put a lot on his plate," defensive coordinator Gus Bradley said. "We felt like his experience he had at linebacker was going to help him do some of the things that we were going to do at strong safety. So we felt that part was a good fit.

"And we also like Nick Cross."

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Colts coaches have raved about Cross' work behind the scenes in his second year since he arrived at training camp and began cross-training at nickel cornerback and free safety in addition to strong safety, work that demanded film time on the players' normal days off. But for the first three months of the season, they struggled to find the right reward or fit, given the youthful makeup of their cornerback room and the chemistry Blackmon and Moore found in the middle line of the defense.

They rolled with Rodney Thomas II at free safety after he surprised as a seventh-round rookie and led the team with four interceptions last season. But as time wore on this year, Thomas struggled outside of his ball skills, resulting in some gashing pass plays as he tried to roam in lots of space as a single-high safety.

The Colts began rotating him with Cross against the Titans in Week 12, after Cross made a third-down tackle from depth against the Buccaneers to help seal a win the week before. Indianapolis planned to stick with that rotation until Blackmon got hurt, which thrust both players into full-time roles and exposed the current reality of the room.

It also showed them Cross was ready to unleash. It's a step from last season, when he was the youngest player on any NFL roster and the Colts benched him in Week 2 for a more experienced Rodney McLeod. This version is focused, but he's still the elite athlete that general manager Chris Ballard sent a future third-round draft pick to take a year early out of Maryland.

Cross would up playing all 75 snaps against the Raiders, compared to just two snaps for Thomas.

“He’s built like a little bulldog,” Harrison said of Cross. “He’s strong as hell. He can play the free or the strong (safety position) and he’s fast. He knows the game. He has good feet. He has good ball IQ. … He’s a good football player all-around.”

Meanwhile, Harrison had been flashing as the team's starting 'WILL' linebacker on base downs. He intercepted Baker Mayfield in the win over the Buccaneers and scored a pick-six against Jake Browning and the Bengals.

"He's just a ball player," linebacker Zaire Franklin said. "Ronnie, I keep telling him, he ain't no rookie. He's a vet. He's made plays in this league.

"He's not afraid of that moment."

The Raiders were starting backup quarterback Aidan O'Connell but had three-time first-team All-Pro wide receiver DaVante Adams to apply plenty of attention toward. Adams caught 13 passes for 126 yards and two touchdowns, but the Raiders spent all game chasing points as no play went for more than 24 yards.

It was a tune-up for what is to come on Saturday, when the Colts battle the Texans in a win-or-go-home game for both squads. C.J. Stroud will be a significant jump up from the quarterbacks the Colts have played lately, as the No. 2 pick in the draft is running away with the Offensive Rookie of the Year Award with 21 touchdown passes, five interceptions and 8.1 yards per attempt. He threw for 384 yards in a Week 2 loss against the Colts.

But Sunday's win over the Raiders was a confidence boost for the new look.

"It's just the preparation that we do every day, day-in and day-out," said Chris Lammons, who filled in for Moore at nickel cornerback. "We have guys that have played linebackers who know what the DBs are doing based on how the coaches prepare us.

"The guys who stepped in are football players. They're going to get the job done."

Contact Nate Atkins at natkins@indystar.com. Follow him on Twitter @NateAtkins_.

This article originally appeared on Indianapolis Star: Colts: How Nick Cross finally beat out Rodney Thomas II