Until recently, one of the 49ers’ stars of the summer had been forgotten in the fall.

Defensive lineman Mike Purcell was a tackle-making machine in the preseason, which allowed him to make the 53-man roster, which allowed him to … sit. And wait.

“It wasn’t terrible,” Purcell said, “but you always want to get on the field. Sitting on the sideline isn’t the best. But when your number’s called, you’ve got to be ready.”

On Sunday, Purcell was clearly prepared when he made his first NFL start in a 19-13 loss to Arizona. The undrafted free agent had three tackles, the 49ers’ lone sack and was part of a stout front that limited the Cardinals to 70 rushing yards and 2.4 yards a carry.

It was the type of ability Purcell, 24, had flashed in exhibition games, but he was inactive for the first eight games of the regular season. On game days, Purcell stood on the sideline in street clothes in September and October.

During the week, however, he was preparing for a chance to finally play. Defensive coordinator Eric Mangini likened Purcell’s professional approach to that of defensive lineman Glenn Dorsey, 30, an eight-year veteran.

“In the last two months, he’s been as consistent as you can get,” Mangini said. “He reminds me of Glenn Dorsey in that way: quiet, but tough. A consistent worker. He’s another guy that you really cheer for because he just keeps working every day.”

As it happens, the biggest opportunity of Purcell’s career came because Dorsey sustained a torn ACL on the first defensive play in a loss at Seattle on Nov. 22. First-round pick Arik Armstead played most of the snaps after Dorsey was injured and the rookie was expected to start against the Cardinals.

Instead, Purcell got the start and played 49 snaps. Armstead logged just 18. Head coach Jim Tomsula said Armstead played limited snaps because of a shoulder injury, which made him probable for the game.

However, Purcell is a better run defender than Armstead and the 49ers were coming off a game in which they allowed 255 rushing yards against the Seahawks. Purcell’s performance could earn him extensive playing time in the final five games, starting Sunday against the Bears at Soldier Field.

“I could see Mike playing a significant amount,” Mangini said. “Not in just this game (Sunday), but through the course of the rest of the season. He gives us depth at end. He gives us depth at nose. So he’ll be playing both of those spots. And he’s a stout guy and his performance has earned him more opportunities.”

Before Sunday, Purcell had played just 63 snaps in four games since entering the NFL in 2013. He’d played primarily at nose guard, the position at which he impressed in the preseason and played at Wyoming. However, he recently began dabbling at tackle in practice.

“I’ve been working it a little bit,” Purcell said. “It wasn’t uncomfortable. It wasn’t what I was specifically working on every day. But when there was a possibility of me playing there, I had to get more reps at it and we went from there.”

Purcell will use the final five games to audition for a larger role in 2016. He was inactive for the first eight games because of the 49ers’ defensive-line depth, but the position group could look far different next season.

Dorsey probably won’t be ready for the start of the regular season, nose tackle Ian Williams will be an unrestricted free agent and defensive tackle Tony Jerod-Eddie will be a restricted free agent. Meanwhile, defensive tackle Tank Carradine has moved outside into a pass-rush specialist role.

However, Purcell isn’t looking beyond the next game, when he hopes to reprise his performance against the Cardinals.

Said Mangini of Purcell’s first NFL start: “He was really good.”

Eric Branch is a San Francisco Chronicle staff writer. E-mail: ebranch@sfchronicle.com Twitter: @Eric_Branch