In the quiet of a nearly empty Chargers locker room in early January, Norv Turner contemplated the ascension of Vincent Jackson, who had for much of the previous three seasons been bound by expectations he had yet to satisfy.

That day, in the Chargers' first playoff victory in 13 years, Jackson caught five passes for 114 yards and a touchdown against the Tennessee Titans. It was his first career 100-yard game and would begin a three-game playoff run in which he had 300 receiving yards, most in the NFL during the last postseason.

That spurt of production has seemingly bled into this summer. Until he missed the past three practices (two days) with “leg soreness,” Jackson was perhaps the most impressive player in training camp. He has been catching almost everything with an uncanny authority, and he seems to be more explosive than at any point in his career, which is now entering its fourth year.

NELVIN C. CEPEDA / Union-Tribune Receiver Vincent Jackson is finally comfortable in the NFL, and it showed when he amassed 300 postseason yards.

The finish to last season and start to this camp has fueled the belief that Jackson is on the verge of fulfilling the potential he brought into the NFL as a second-round draft pick in 2005, so full of confidence and talent and a physical freak who could run well at 6 feet 5 and 240 pounds.

“This offseason was his best,” quarterback Philip Rivers said. “He finished last season unbelievable, and now he seems more explosive, bigger, stronger. And I don't know how he can get much bigger and stronger.”

No one inside the Chargers organization is surprised Jackson is doing what he is doing – and doing it when he is doing it.

On that January night, after a game in which Chris Chambers caught six passes for 121 yards, Turner said this:

“You know, Vincent is ahead of where Chris was when I had him in Miami.”

Turner was the Miami Dolphins' offensive coordinator in 2002 and 2003, Chambers' second and third seasons in the NFL.

“It takes awhile to get comfortable as a receiver in this league,” Turner said.

Chambers concurred with Turner's assessment and reasoning.

“As far as knowing the game, route running, I'm still learning,” said Chambers, a Pro Bowler in 2005 who came here in a trade last October and caught 51 passes for 833 yards in 13 games (including playoffs). “The last two or three years I'm just getting to know all that.”

There is another man at Chargers Park who knows a little something about progress as a receiver. He has spent more than 20 years as a coach, and before that played receiver in the NFL for 18 seasons.

Chargers receivers coach Charlie Joiner is in the Hall of Fame. His 12,146 career receiving yards are still 15th-most in NFL history.

Now, Joiner was drafted as a defensive back and played a little on that side early in his career. And no one is saying Jackson is Joiner. But the numbers at the start of Joiner's career are strikingly similar to those of Jackson, and they illustrate a point that receivers, especially, ought not be too quickly judged.

“Very seldom does a receiver come in and make a big impact their first year,” said Joiner, who over his first three seasons had 39 more yards than Jackson has in three seasons. “A few do, but those are special guys. Most of the time you come in and you learn, because you've got to read defenses, you've got to learn a new offense. Once you get familiar with the offense and the calls and get used to the quarterback and his throws, and he gets to know you, after about two years . . . That third year you see a lot of guys flourish.”

Jackson shrugs at the suggestion he is miles ahead of his rookie season, which was stunted by some nagging injuries.

“I make progress every year,” he said. “Every year you grow more comfortable.”

That comfort would seem to be the thing.

Certainly, the fact Antonio Gates was knocked from the Tennessee game and then served as a mere decoy in the ensuing two playoff games allowed Jackson to step up.

Moreover, though, Jackson grew comfortable over 2006 and '07 – in the offense and with Rivers.

“It took us some time,” Jackson said. “As much as we've been around each other, it took us time to get a feel for each other, to get confidence and timing down. Last year we clicked at the right time.”

In doing so, Rivers found a third receiver – along with Gates and Chambers – that he knows so well he will throw him a dangerous pass or a pass on feel alone.

“You start to get a feel for a guy – where to put it, where he likes it,” Rivers said. “That grew last year, and it has continued.”

That, in part, is why Jackson is sitting now. His injury is not serious, just enough soreness for there to be caution.

“I don't want to push it and have it linger,” Turner said. “He's off to as good a start as you could hope for.”

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Kevin Acee: (619) 293-1857; kevin.acee@uniontrib.com