SANTA CLARA — Still lurking among the perceived ruins of the 49ers defense is a once-dominant player, one primed for a breakout season: Aldon Smith.

Through offseason practices and the start of training camp, Smith is flashing the form that produced 42 sacks in 43 games from 2011-13.

Early in Sunday’s session at Levi’s Stadium, Smith was at it again, signaling a would-be sack of Colin Kaepernick near the goal line if this had been an actual game.

“One of the greatest challenges I face all year is going against Aldon,” left tackle Joe Staley said Friday upon reporting to camp. “He is, in my opinion, the best outside linebacker in the NFL.”

Last year, Smith had only two sacks, both coming in his second game back from a nine-game suspension. But now, his career should emerge from the stall that accompanied his off-field issues, including a 2013 drunken-driving accident and its ensuing fallout.

Neither Smith nor coach Jim Tomsula is overselling this idea. Instead, both voiced a humble approach, Smith going only so far as to say: “My body feels well, and I’m ready to go.”

Unlike two years ago, there’s no chatter about Smith chasing the NFL’s single-season sack record (still at 22﻿1/2, by Michael Strahan in 2001). But unlike the past two years, there’s no sign of Smith in police reports or court dockets.

“I’m really happy for and excited for Aldon,” Tomsula said. “I respect what Aldon is doing, and I respect the road he is on.

“Life throws things at you, man,” Tomsula added. “Sometimes you cause them, sometimes you don’t. But things happen. To me, the answer is always in you … and how you handle it and where you go from there. Own it, fix it, and let’s go.”

Smith, 25, looks to be in the best shape of his five-year career, and he confirmed things are “real good.”

That could translate into improved production with long-term benefits. This is his final year under contract, one which he restructured to earn his $9.75 million in increments. Last month produced megadeals for two outside linebackers: Kansas City’s Justin Houston (six years, $101 million) and Washington’s Ryan Kerrigan (five years, $57.7 million).

A rejuvenated Smith is certainly appealing for Eric Mangini, the 49ers’ new defensive coordinator who spent the previous two years as an offensive assistant.

“When you’re on the other side of the ball like I was and you’re watching one-on-one pass rush — and working with the tight ends last year, where they had to block him in some of those one-on-one pass rush — you appreciate just the volume of moves that he has,” Mangini said.

Mangini hinted he may move Smith around in the defensive front, which isn’t a totally new concept but one that must be explored while the line adjusts to the departures of Justin Smith and Ray McDonald. Aldon Smith said he’ll be “comfortable with whatever.”

“Anybody that’s filling Justin’s spot, we’re going to have to create a chemistry with, because that’s the guy who’s been beside me since I’ve been here,” Smith said. “But people learn fast.”

The most logical wingmen are Glenn Dorsey, Quinton Dial and Tank Carradine. Dial was the right defensive tackle next to Smith in Saturday’s base-defense alignment. Other key linemen are Tony Jerod-Eddie, Ian Williams and two newcomers: Darnell Dockett, likely in the nickel package, and Arik Armstead, this year’s first-round draft pick.

“If anybody underestimates us, that’s their problem,” Smith said, “And we’ll be where we need to be when the season gets here.”

Kurt Warner, observing practice as an NFL Network analyst, insisted on taking no credit for Kaepernick’s apparent development, even though they worked together this offseason in Arizona. “Yeah, you’re starting to see him begin to understand playing the quarterback position a little more,” Warner said. “(There) is the ability to throw with touch, the ability to anticipate things.” Warner stressed that Kaepernick’s biggest challenges are to get comfortable in the pocket, to pin down the time needed for his progressions, and to figure out when to run. Said Warner: “You just can’t live in that create-a-play world in the NFL, no matter how good you are. Six or seven times a game, maybe. But to try to live there 20 to 25 times a game, that’s not where you’re going to be. That’s going to always be the biggest challenge for an athletic guy.”

More divots came up on Levi’s Stadium’s embattled sod, but that did not appear to hinder practice or cause any injuries.

Bruce Ellington, sidelined in the offseason program with a hamstring issue, flashed his speed and play-making skills at wide receiver and as a return specialist, his roles last season as a rookie.