SANTA CLARA - If Nnamdi Asomugha is the 49ers' biggest mystery entering the 2013 season, the Packers ought to provide an early answer Sunday at Candlestick Park.
In last year's Week 1 game against the 49ers, Green Bay quarterback Aaron Rodgers threw a season-high 44 passes. In a rematch during the playoffs in January, he put the ball in the air 39 times.
"They throw 99 percent of the time," Asomugha said, exaggerating slightly. "So the ball will be up in the air a lot."
More importantly regarding Asomugha, the Packers were in three- or four-receiver formations on 88 percent of their offensive plays in the two losses last season. In those instances, the 49ers' No. 3 cornerback goes into the game and the nose tackle - Ian Williams this year - comes out.
Last season, then-No. 3 cornerback Chris Culliver mostly covered wide receiver Jordy Nelson, a winning matchup for the 49ers.
In the first game, Rodgers targeted Nelson only twice when Culliver was covering him, according to Pro Football Focus. Nelson caught one pass for 7 yards, and Culliver knocked away a pass to Nelson late in the fourth quarter to seal the win.
In the rematch in January, Culliver gave up one catch for 10 yards, according to PFF, but also was called for pass interference against Nelson.
Asomugha, this year's No. 3 cornerback, should see plenty of Nelson on Sunday.
"Yeah, (Asomugha) will probably be on him a good bit of the time," defensive coordinator Vic Fangio said Thursday. "We basically are playing left and right with our corners in the (nickel defense), but they like to line their receivers up from left to right also. So, yeah, a good chance that he'll be on him for a fair amount."
Asomugha has been dealing with a collarbone injury suffered Aug. 25 against Minnesota, but Fangio said he'll play against the Packers, barring a setback.
Asomugha, 32, a four-time All-Pro, is the 49ers' best-known free-agent acquisition, but he is coming off two down seasons in Philadelphia during which he often was beaten deep.
In the preseason, however, Asomugha allowed only one reception, for 5 yards on third and 12. He did not play in the Aug. 29 finale.
Asomugha has played 10 seasons, but he's never faced Rodgers, a fellow Cal product. Asomugha faced the Packers when he played for the Raiders in 2007, but Brett Favre was Green Bay's starter then.
"They kind of let him do his thing with the offense," Asomugha said of Rodgers. "The top quarterbacks in the league have control of the offense, not that they do different things, but they let the quarterback do all the checks, make all the calls."
Read Matthew Barrows' blogs at www.sacbee.com/ sf49ers and listen for his reports Tuesdays on ESPN Radio 1320.