ALAMEDA, Calif. -- Khalil Mack's eyes narrowed as he crouched into a two-point stance in early September. Standing across from the Oakland Raiders outside linebacker was Houston Texans Pro Bowl left tackle Duane Brown, a 6-foot-4, 320-pound mammoth of a blocker eager to test a first-year player in a game that was quickly turning into a Houston blowout. But as soon as Brown fired across the line of scrimmage after the snap, the 6-3, 252-pound Mack deftly slid away from the oncoming lineman, then easily tackled Texans running back Alfred Blue for no gain.

A few plays later, Mack was even more determined, as he noticed Texans backup tight end Ryan Griffin lining up across from him. I played against this guy in college, Mack thought to himself. If he's out here, I know I can play this game at a high level. Mack easily tossed Griffin aside on a couple more runs to remind the former UConn player that little had changed now that they were competing on football's biggest stage.

In fact, the longer Mack played in that 30-14 Week 2 loss, the more he felt as though he was making a statement with every play. The Raiders may not have been winning, but the rookie was telling the world something about a player who had been selected fifth overall in the 2014 draft. "I learned early on that it's hard to win games in this league," Mack said. "You have to pay attention to detail. You have to always have the right technique. And you really do have to play every down like it's your last."

Khalil Mack wasn't satisfied with four sacks last year. "Those sack numbers I had really weren't me," he said. AP Photo/Gregory Bull

The lessons Mack learned during his rookie season undoubtedly will come in handy this fall. There are still many questions surrounding a Raiders team that hasn't enjoyed a winning campaign since 2002 -- including the mysterious hand injury that has hampered second-year quarterback Derek Carr throughout organized team activities -- but one spot the franchise shouldn't worry about is strongside outside linebacker. At 24 years old, Mack already has flashed so much potential that Raiders safety Charles Woodson told the San Jose Mercury News last season the "dude is going to be special."

In his first season, Mack finished with 75 tackles, four sacks and a forced fumble, numbers that helped him finish third in voting for the league's defensive rookie of the year award (behind St. Louis' Aaron Donald and Baltimore's C.J. Mosley). This year the Raiders have much bigger expectations for Mack, especially with new head coach Jack Del Rio starting his first season and defensive coordinator Ken Norton installing new schemes. Del Rio wouldn't give many specifics on how Mack's role would change but he did make it apparent that Mack won't spend nearly as much time in pass coverage as he did in 2014. This time around, Mack will be chasing quarterbacks as much as possible, which is something he did quite well when given the chance, even if the sack totals don't look significant. Mack had 40 QB hurries last season to go with his exceptional defense against the run.

Since Del Rio coached Pro Bowl outside linebacker Von Miller as the Denver Broncos defensive coordinator from 2012-14, he'd like to see Mack have a similar impact on opposing passing attacks. "I think Khalil is way more physical than Von," Del Rio said. "Von got up to somewhere around 250 pounds when I had him but he's naturally closer to 240. Khalil can be up around 260 or 265 and they both play that strongside linebacker position and sub-pass-rusher role. Since most teams use their sub packages for two-thirds of the game, there will be some opportunities there. They're different but they're both special."

"I definitely want to get after the quarterback more this year," Mack said. "I got some hits [in 2014], but people didn't really see what I can do. Those sack numbers I had really weren't me. At the end of the day, you want people to see you at your best."

That explains why Mack didn't spend his offseason in trendy hot spots such as South Florida or Scottsdale, Arizona, the typical areas where many young NFL players prefer to train. Despite being a Florida native -- Mack grew up in Fort Pierce -- he returned to the University of Buffalo to work out with trainer John Opfer. When Mack wasn't running steep hills or lifting weights with his former college teammates, he was focusing on areas that could fine-tune his physique for a strong second year. Some of the most vital elements of Mack's conditioning program involved strengthening his hands (so he can shed blockers far more easily) and building his core muscles (to increase his overall explosiveness).

Mack finished third in defensive rookie of the year voting. Kirby Lee/USA TODAY Sports

Why train in upstate New York? "It's very easy to focus in Buffalo," Mack said. The decision speaks volumes about his approach to his career in general. Mack's road to the NFL was filled with several setbacks and plenty of people who questioned if he'd ever be a difference-maker in college. The last thing he wants to do now is forget the same ideals that brought him this far in the first place.

As Mack recently leaned against a wall outside the team's training facility following an organized training activity session, it wasn't hard to see the appreciation he has for his current standing. He laughed when thinking about this time of year last season, when he walked into the locker room for his first minicamp and bumped into defensive end Justin Tuck, a veteran of 11 NFL seasons. Tuck told Mack that he was impressed with his game, then offered a bit of invaluable advice. "Whatever you do this year, just shut up and listen," Tuck said. "You're a great player, but you don't have any idea of what you're doing yet."

That suggestion helped Mack understand that his road to success in pro football would come down to how well he did the little things -- such as studying film and refining his techniques -- instead of overwhelming opponents with jaw-dropping athleticism. It was a lesson quite similar to the one he learned while growing up in a deeply religious, two-parent household, with a father who worked as both a program specialist and a deacon. Sandy Mack Sr. had long ago counseled his son to spend more time listening to his elders than speaking his mind. In his father's eyes, that was the best approach for young Khalil to find his way through the hurdles that eventually would challenge him.

That combination of humility and faith helped Mack when a torn patella tendon ended his hopes of earning a basketball scholarship when he was only a sophomore at Fort Pierce Westwood High. It also meant plenty when he was a lightly regarded football recruit who wound up at Buffalo only because the coach who was previously recruiting him to Liberty University took a job at that program. Of course, there's also the story of why Mack wore number 46 in college. He donned it because the video game "EA Sports College Football 10" had given him a rating of 46 (an extremely low mark) before he started his redshirt freshman season in 2010.

Mack ultimately became an All-American by his senior year and left Buffalo as the NCAA's career leader in forced fumbles and tied for career tackles for loss. "I don't know if Khalil really understood all his talents when he was in high school," said Opfer, who also has become a mentor to Mack. "He didn't go to the big [exposure] camps in the summer, and he didn't play competitively until his junior and senior years. So to have that little experience and end up blowing up college football says a lot. When he started to believe he could be great, that's when he took off."

Still, all that success in college had some repercussions once Mack arrived in Oakland. When his first NFL season began, he found himself pressing to make the same splash plays that had defined him in college. " I knew the only way to make a strong impression was to make the big plays," Mack said. "But I wasn't making the same plays I was making in college when I first got here. Eventually I had to understand that this is a group effort. We all have to be involved in order to make the plays we need to make."

Mack registered 100 tackles and 10.5 sacks his senior season at Buffalo. Timothy T. Ludwig/USA TODAY Sports

Just as difficult for Mack was grinding through a season during which the Raiders won only three games. He leaned on the wisdom of veterans such as Tuck and Woodson, but Opfer also saw a player who learned how to play as the season progressed. "Khalil is a smart guy, but he got away with being a read-and-react player in college," Opfer said. "He had so much God-given ability that he could miss a read and still react fast enough to make a play. But as last season went on, you saw his football IQ grow. He became a lot more proficient at putting himself in the best possible positions to make plays."

Mack drew plenty of praise in the process. Seattle Seahawks coach Pete Carroll told reporters last season that Mack "jumped off the film" when his staff studied the Raiders. Former Cleveland Browns quarterback Brian Hoyer, now with Houston, said Mack was one of the best players that team faced in 2014 and added that "he gained the respect of everybody on our team." Del Rio said the Broncos had similar impressions. "Our offensive guys always wanted to know where he was," Del Rio. "That tells you a lot about what he can do."

Now the Raiders need to see even more growth as Mack heads into this coming season. The popular belief in the NFL is that players show the greatest improvement between their first and second years in the league, which means Mack should be poised for a huge leap in productivity. That goal weighed heavily on his mind whenever he strapped on a weighted vest in Buffalo this offseason and trudged toward a steep hill near the facility where he trained. Joined there by former Buffalo players such as San Diego Chargers running back Branden Oliver, Mack charged up that incline at least three times a week, all with the hopes of chiseling his thick legs and testing his willpower.

Mack had followed a similar routine in college, when he helped the Bulls grow from a program that won two games during his freshman season to one that finished second in the MAC during his senior year. A similar challenge now awaits him in Oakland. The Raiders know they still have plenty of changes to make in order to become a playoff contender. But if Mack can become the foundation of a young defense, that task will prove to be much easier.

"I can definitely say we will be relentless on defense this year," Mack said. "We're going to be dominant and physical, and we're going to fly to the football. That's what this game comes down to -- playing with that kind of effort. And we want to be the kind of defense that takes the ball away and gives it back to our offense as much as we possibly can."