Green Bay opens the preseason at San Diego, site of Mike McCarthy’s first game as head coach back in 2006. The Packers lost that game, 17-3, but they've obviously gotten better since.

The Packers beat the Chargers, 45-38, last year in route to a 15-1 regular season but lost in their first playoff game. That disappointment and failure led to an offseason spent upgrading the defense (on paper, at least) and trusting that the offense will be as prodigious as before.

The preseason opener is the first real test for the young, unproven and new players the Packers are trusting to be the nuts and bolts of a reconstructed defense.

Here are three things to keep an eye on Thursday night:

1. Harrell’s command of the second string: QB Graham Harrell has been given the backup job after serving as practice squad/third string quarterback for two seasons. He’s got the mental capacity and arm to do the job, but does he have the poise? He’s never looked comfortable dealing with pressure and, with a patchwork offensive line and less-skilled receivers on the second team, there’s a lot of pressure to deal with. It’s clear he can cope with one kind of pressure. Last year, he marshaled the Packers to 11 points in the final 35 seconds in a come-from-behind win over the Colts in the third preseason game. In that game, he threw an 11-yard touchdown pass on fourth-and-10 to TE Ryan Taylor, connected with Taylor again for the two-point conversion and then, after Green Bay recovered the ensuing onside kick, got the offense in position for a last-second, game-winning field goal. But can the spread-offense college QB remain composed and accurate in the face of hungry pass-rushers? For the Packers to win Thursday, he’ll have to, since starter Aaron Rodgers will exit early.

2. Some kind of pass rush: Last year, the Packers lacked any semblance of a pass rush. It ultimately doomed them. The Packers added a few free agents and a couple of highly touted rookies to the mix in the offseason and Thursday is the first chance to see if anything’s changed. Veterans B.J. Raji and Ryan Pickett are the only sure things; after that, there are lots of bodies, plenty of competition and ample opportunities. Voluble free agents Anthony Hargrove and Daniel Muir will get reps, as the coaching staff evaluates how they can contribute. Second-round pick Jerel Worthy and fourth-rounder Mike Daniels, who’s questionable with a leg injury, can expect a bulk of playing time, too. And don’t forget about incumbents C.J. Wilson and Jarius Wynn, who are out to prove they deserve a spot on the retooled line. Oft-injured DE Mike Neal, who’s suspended the first four games of the season, has been playing like a guy with an angry vengeance. Lawrence Guy, an injured practice-squad player from a year ago, has talent and size but needs to make some splashy plays to get noticed. Phillip Merling, a disappointment since he was drafted five years ago, has done nothing yet to warrant consideration. There are literally more than enough competitors in camp; the Packers need some of that girth to show it can rush the passer.

3. Special teams standouts: The Packers are set at the specialist positions -- K Mason Crosby and P Tim Masthay are both consistent and signed through 2016 -- but coverage and blocking units remain open to applicants aspiring to play professional football. Coach Mike McCarthy and QB Aaron Rodgers have reiterated that the surest way onto a crowded, talented roster like Green Bay’s is through special teams proficiency. A kick return for a touchdown by embattled CB Sam Shields? A downed punt by an undrafted gunner at the 2-yard line? A couple of gritty blocks on a return? Those are the kinds of plays that get unknown players noticed by coaches. It’s simple for special teamers: make plays to make the team, get noticed and get the victory. It’s win-win.

For more news and notes on the Packers, follow James Carlton on Twitter @CBSSportsNFLGB.