SANTA CLARA, Calif. (AP) When projecting the San Francisco 49ers' roster in the spring, defensive lineman Mike Purcell was a long shot.

After all, the former undrafted free agent spent most of the last two seasons on the practice squad while the team signed notable veteran Darnell Dockett and used a first-round pick on Oregon's Arik Armstead. At nose tackle, where Purcell spends the most time, Ian Williams and Glenn Dorsey were returning after missing significant chunks of 2014 with injuries.

But after a strong preseason, including a rare touchdown scored off an interception, Purcell, 24, cracked the 53-man roster. Dockett, 35, was released after playing 16 snaps, despite signing a two-year deal in March.

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Purcell led the 49ers defensive line with 17 tackles over four exhibition games, including two for loss.

He got off to a strong start with a six-tackle performance in the preseason opener in Houston that included playing a pivotal role in an eight-play goal line stand in the first quarter, when the 49ers forced a turnover on downs.

Purcell backed that up the next week by intercepting Cowboys quarterback Dustin Vaughan and returning it 37 yards for the touchdown. ''He made the play and he took off. That's the fastest I've seen him run, I'll tell you that,'' first-year head coach Jim Tomsula said afterward.

Tomsula is very familiar with Purcell after being his position coach since he joined the 49ers out of Wyoming following the 2013 draft. Under Tomsula's tutelage, Purcell evolved from practice squad afterthought to viable roster candidate.

''I think I've just grown overall, on and off the field,'' Purcell said. ''In the books and when it comes down to game day. You can always practice well, but if you don't carry it over into the games, it doesn't really help.''

A significant portion of Purcell's growth away from football came with the birth of his son, Kaimana, seven months ago. Kaimana and Purcell's wife, Christina, were regulars at the team's facility during training camp, serving as reminders of what was at stake.

''I think that was one thing that really hit him and hit home,'' said Williams, a captain of the defense. ''It was like, `I got my little man in the world now.' I can attest to that because I have my daughter and my son. I know (Purcell) is excited about the season. He's been working hit butt off and he's ready to go out there and show 49ers fans what he can do.''

Purcell joins a list of formerly unheralded defensive linemen to make an NFL roster coached up by Tomsula that includes Williams, Tony Jerod-Eddie, Quinton Dial, Washington's Ricky Jean-Francois, and Seahawks Demarcus Dobbs and Will Tukuafu.

Those players had something in common that Tomsula was able to identify, Purcell included.

''I don't need anybody that blinks,'' Tomsula said. ''.I'm going to be more demanding on you. I'm going to have meetings at 11-o'clock at night. I'm going to take you all the way to curfew with meetings because I'm trying to get you to a place to survive, to make it.''

NOTES: Tomsula said Tuesday that 49ers players named nine captains in a team-wide vote: QB Colin Kaepernick, LT Joe Staley, WR Anquan Boldin, TE Vernon Davis, LB NaVorro Bowman, DL Williams, S Eric Reid, S Antoine Bethea and K Phil Dawson. However, those players will not wear captaincy patches on their uniforms. ... Tomsula indicated second-year players CB Kenneth Acker and CB Keith Reaser are still battling to start opposite CB Tramaine Brock in the Sept. 14 season opener against the Vikings. ... RB Jarryd Hayne, WR Bruce Ellington and WR DeAndrew White are all possibilities to return punts and kickoffs, according to Tomsula, who said the team has made its decision but will not reveal it.

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