INDIANAPOLIS -- The transition was supposed to be a methodical one for Indianapolis Colts rookie running back Jonathan Taylor.

He’d get his fair share of snaps while backing up starter Marlon Mack throughout the season as he got used to playing in the NFL instead of the Big Ten.

But after one play and one pop of Mack’s Achilles, Taylor went from backup to starter. Coach Frank Reich said Taylor will move into the starting role after Mack was lost for the season because of a torn Achilles suffered in the first half Sunday against Jacksonville.

"Marlon is beloved in our locker room," Reich said. "[The team has] such an immense amount of respect and love for this guy. He’s a true Colt. He was looking so good in training camp and even in his few snaps [against the Jaguars]. Very unfortunate and very bad timing for him and his family."

Now the final 15 games of the season are basically an audition for Taylor. The NFL is a business, and the reality is that Mack, unfortunately, will be a free agent -- a free agent coming off a torn Achilles -- during the offseason. That means Taylor needs to use this time to prove that he can be the primary running back for the Colts going forward.

His first test comes Sunday against the Minnesota Vikings.

“Jonathan is ready,” Reich said Monday. “He’ll step up and do a great job. ... I think it’s a mindset that Jonathan has to come in and just take ownership of the position. We’re still going to rotate guys through, but Jonathan still has to be lead dog and have that mindset and confidence, and I know he’ll do that.”

The Colts knew about Taylor’s talent. That’s why he was their second pick in the second round back in the spring. He used a combination of strength and speed to rush for 6,174 yards, including back-to-back 2,000-yard seasons, in his three-year career at Wisconsin.

The Colts’ commitment to running the ball is evident in the depth they have at the position. Taylor will be the primary back, with Nyheim Hines used in the passing game and Jordan Wilkins brought into the mix as the third running back.

“I think coach Reich has done a great job, not only through training camp, but this started before training camp, making sure that I was up to speed as much as possible,” Taylor said. “Not being able to have OTAs and not being able to have rookie minicamp, we had to try to do as many meetings as we could and also add on top of that throughout training camp to try to get me up to speed with those vets.”

Taylor didn’t touch the ball for the first time until the second quarter Sunday. That first touch ended up being a 36-yard gain on a screen pass. Taylor had 22 yards rushing and 67 yards receiving in his NFL debut.

The Colts had only 22 rushing attempts against the Jaguars. You can expect that number to increase in the coming weeks because they don't want to rely on quarterback Philip Rivers to throw the ball 46 times a game.

The Colts will miss Mack because he's experienced, fast and coming off his first 1,000-yard season. But Taylor has some of the same attributes, which is why Reich described both as No. 1 running backs before the start of the regular season.

"You can feel not only [Taylor's] speed on the field, but you can feel his size," Reich said. "So that combination of speed and size equals power and force, and I think we’ll see that. We’ll feel that. It’ll add to what is already a physical offensive line. But the great thing about Jonathan, unlike a lot of backs, who bring that physicality, Jonathan also brings breakaway speed.

"What I’m hoping to see, which is why we have to continue to call more runs, is that you get a guy who can be a workhorse back like that. The more times you give it to him, the better they’re going to get, more confidence they’re going to get. That's going to be another reason why we have to continue to feed the running game."