Arik Armstead can't believe it's been five months since he first arrived at the SAP Performance Facility.

On April 30, the San Francisco 49ers selected the defensive lineman out of Oregon with the 17th overall selection. Since then, Armstead has gone through a rookie minicamp, training camp and now is three games into his rookie season.

"Time has flown by. Looking back at it, I didn't realize that was five months ago," Armstead said. "Everything is moving fast, but I'm getting comfortable around my teammates and my coaches. I'm getting settled in."

Armstead said the transition from being a student athlete to a professional has been his greatest challenge. The rookie credited his fellow defensive linemen with helping him mature and balance the added responsibilities of being a player in the NFL.

"The whole d-line group has embraced me," Armstead said. "I asked them a bunch of questions. I love learning from them on and off the field. They're always there to help me."

The former Oregon Duck is already seeing his role increase within Eric Mangini's defense. In his NFL debut against the Minnesota Vikings, Armstead played 12 snaps. The following week against the Pittsburg Steelers, Armstead saw 14 snaps. Most recently, the rookie played 18 snaps against the Arizona Cardinals.

The extra reps have come with production as well. Armstead has five combined quarterback pressures over the last two weeks and recorded his first career sack against the Cardinals. The play also marked the first time Carson Palmer had been sacked all season.

"It was big," said Armstead, who had three tackles in Week 3. "It was huge to get my first career sack. The game didn't end up the way we wanted it to, but it was my first sack for my career and I hope to have many more."

Back-to-back decisive losses for the 49ers could open the door for Armstead to build himself a bigger role in the gameplan. The rookie can't control the decisions that the coaching staff makes, but Armstead hopes his play will speak for itself in his case for more playing time.

"I'm going to control what I can control and that's going out there and playing as hard as I can," Armstead said. "(I'm) trying to make plays and help my team win games. Whenever they throw me out there that's what I'm gonna try to do."

Back in April following Armstead's seleciton, Jim Tomsula said he wanted the rookie to be able to rush the passer and stop the run. The 6-foot-7 defensive lineman's performance against the Cardinals showed glimpses of fulfilling those hopes.

Now it's all about fine tuning those skills and being consistent.

"I'm young, and I have a lot to improve on and a lot more room to grow in all aspects of my game," Armstead said.

In the 49ers 3-4 defensive scheme, Armstead rushes between the offensive tackle and offensive guard, otherwise known as the "B" gap. The Sacramento, Calif., native broke down the keys to rushing the passer between the tackles.

"It's being quick," Armstead explained. "It's tight spaces when you're inside. When you're on the edge, you have a little more time to set up moves and things like that. It's about being physical, violent and quick in those tight spaces."

Next up for Armstead and the 49ers defense is Aaron Rodgers and the high-octane Green Bay Packers offense.

Green Bay put up 38 points on the Kansas City Chiefs in Week 3 and will provide the 49ers with another tough test. That said, Armstead can't wait to chase around one of the best quarterbacks the NFL has to offer.

"I'm looking forward to it," Armstead said. "They've got a good offensive line, a good quarterback and a good offense in general. It's going to be a challenge for us, but I'm looking forward to my first time playing against them."