SANTA CLARA (AP) — As devastated as Ian Williams felt two years ago when he went undrafted out of Notre Dame, he can now look back on that moment and realize how much the rejection meant to his career.

He landed with the San Francisco 49ers, and is the leading candidate to win the starting nose tackle job for the NFC champions as he begins his third NFL season.

“It hurt, but looking back at it, it was probably the best situation that could have ever happened,” Williams said after a recent practice. “I was a young kid, expecting this, expecting that. It kind of put me back to my place, and coming here and getting back to work really propelled me to where I am now.

“I lost sight of the goal that I set. Drastic things usually get you back on track.”

The expectations for Williams are high heading into the team’s exhibition opener Thursday night at home in Candlestick Park against Peyton Manning and the Denver Broncos.

San Francisco lost both its starter and backup at the position to free agency this spring, leaving Williams and veteran newcomer lineman Glenn Dorsey to push each other in training camp — yet Williams has more experience. Dorsey could spend some time at defensive end, too.

Williams prepared himself for this opportunity by losing 25 pounds from his previous playing weight during the offseason, bringing him down to 305 and right where he hopes to stay this season. Defensive coordinator Vic Fangio has noticed an improvement in Williams’ agility and quick step off the snap.

“I can feel a great difference. We haven’t been in a game yet, but just being out in practice and working out here just really got me ready and going against our O-line the past two years has really gotten me ready for what I have in front of me,” Williams said. “Toward the end of the season it gets cold out here and it’s hard to sweat and you’re still eating two or three times a day, so it’s hard to lose weight. Then the offseason came and I worked hard, I stayed here.”

To this day, Fangio can’t point to exactly why Williams wasn’t drafted. Perhaps his 6-foot-1 height caused NFL teams to shy away.

“Every year you see that happen. Why wasn’t he drafted at least in the seventh round the year he came out? I don’t know,” Fangio said. “I don’t know if there were some questions about his work habits. Obviously, he’s on the short side as most D-linemen go. I don’t have a good answer for you there. Trust me, he should have been drafted.”

Williams, with shoulder-length braids, has played in four games total. That hasn’t kept the 49ers from believing he is ready to take on a starting role.

And Williams always stayed upbeat as he paid his dues buried on the depth chart and regularly inactive for game days during his first two seasons.

“It was vital to where I am right now,” he said. “Just coming into a good situation and having a veteran crew around me and guys who really took me under their wing and taught me even though I was coming in to compete at the position, I really came into a great situation.”

In March, that situation became even better when Williams received a two-year contract extension carrying him through the 2015 season.

That vote of confidence meant a lot to Williams, who has seven career tackles as he approaches his 24th birthday later this month.

“I really wasn’t worried about getting paid for the contact. It just showed me that I had to get back to work and work even harder,” he said. “Tasting the Super Bowl and getting that close to a ring, to a victory, that got me hungry. The contract extension got me even hungrier. I’m not even worried about all that. I’m just trying to come back, compete, work and try to get back to another Super Bowl.”

Williams keeps in touch with both Isaac Sopoaga, now with the Eagles, and Colts defensive lineman Jean Francois. He tries to learn from Justin Smith and Ray McDonald each day.

He also appreciates regular feedback from linebackers Patrick Willis and NaVorro Bowman.

“It’s really his knack for being able to move. A lot of times people think nose guards are guys that are just big and just hold a point,” Willis said. “But he’s a guy that if you single him he can beat you 1-on-1. If you double-team he can hold the point. As a middle linebacker, that’s what you love to see.”

Notes: The 49ers signed P Colton Schmidt to a three-year deal and waived WR Charly Martin. ... In Thursday’s game, Demarcus Dobbs is slated to start in place of Justin Smith as the All-Pro Smith nurses an injured finger. Fangio also said Craig Dahl, the former Rams S signed to a three-year contract in March to help fill the void of Dashon Goldson’s departure, will start at free safety and rookie Eric Reid will enter later.