FRISCO, Texas -- There was a time when Dallas Cowboys defensive end Aldon Smith was mentioned with Pro Football Hall of Famers.

He recorded 30.5 sacks in his first 27 games with the San Francisco 49ers, becoming the quickest pro player to reach 30 sacks. Reggie White, a defensive end with the Philadelphia Eagles, had held the mark with 30 sacks in his first 28 games.

Also, Smith recorded 33.5 sacks in his first two seasons with the 49ers, the most in the first two seasons by a player in NFL history. In his first three seasons, he had 42 sacks, bettered only by White, who had 52, and Hall of Fame linebacker Derrick Thomas, who had 43.5 in his first three seasons with the Kansas City Chiefs.

Just how good was Smith at the start of his career?

"Got me a pay raise," said Cowboys defensive line coach Jim Tomsula, who coached Smith when both were with the Niners. "[He was] very good. Very good."

Off-field issues and suspensions derailed Smith's career from its potential Hall of Fame trajectory. He has not played in a game since Nov. 15, 2015, with the Oakland Raiders. Smith has had 13 practices with the Cowboys (through Monday), and there are signs he still can be an effective piece to their new-look defense under coordinator Mike Nolan.

"If you walked away from practice, you'd say, 'Hey, who the hell was No. 58?'" Cowboys coach Mike McCarthy said.

Smith wore No. 99 during his five years in the league. Now, he wears No. 58 for the Cowboys. Back then, Smith was 255 pounds. Now he is listed at 280 pounds. Back then, Smith was more of a speed rusher (although he personally might disagree). Now, he has the power of a defensive tackle and the speed of a defensive end.

"Aldon, a lot of times you get things, when the game happens naturally for people, they just kind of sit on that natural instinct," Tomsula said. "He's one of those rare individuals that it comes very natural to him but then he also works at it. He's trying to improve. Every day is a work day."

The Cowboys had no idea what they were getting when they signed Smith to a one-year deal that could pay him as much as $4 million. He quickly showed he could help.

In his first practice, he used his 35 3/8-length arms to deflect and nearly intercept a lofted screen pass from Dak Prescott. A few days later, he was in the quarterback's face, bringing pressure off the edge. On one play, he saw through the diversion of a reverse and waited for the receiver to come his way. On another, a blocker simply crumpled to the ground as he tried to block Smith.

"It's something I never really lost," Smith said "It's something I've always been able to do, so it wasn't too tough to get back into."

If the Cowboys had concerns about rust or Smith's conditioning, they have not showed it. Smith has not had a day off from training camp nor a cut in snaps. McCarthy did not want to get into how much or how little Smith will play when the season starts, but he has been impressed.

"You just see the instincts that he plays with, his ability to recognize blocks and just things that he obviously did at a very high level back in San Francisco," McCarthy said.

Tyron Smith has been named to the Pro Bowl in each of the past seven seasons, and he is considered one of the best tackles, if not the best left tackle in the NFL. In past camps, he has been asked to block DeMarcus Ware and DeMarcus Lawrence, and he has come away impressed with Aldon Smith.

"Don't really know how to describe it, but he's a variety type of player," Tyron Smith said. "He can bring any kind of move that he wants. You can tell that he has that experience. You can tell that he has a love for the game. Just kind of difficult how to describe him. You just never know what he's going to bring to you."

The Cowboys' season opener against the Los Angeles Rams is less than two weeks away. It will be Aldon Smith's first game in the NFL in 1,764 days. He swears he is not thinking about sacking Rams quarterback Jared Goff or going against left tackle Andrew Whitworth.

Before his first practice, Smith said he was excited and said it was surreal to be back in the NFL and with the Cowboys. However, he did not want to admit those feelings to his teammates.

"Just staying in the moment and living each day," Smith said. "I don't want to ever get ahead of myself. I'm grateful for every day and with that gratitude how I want to give it back is by giving and putting everything into every day and focusing 100 percent so when that day's over I don't look back with any regret."