Will Aaron Rodgers feast on 49ers’ defense?

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In one corner, we have Packers quarterback Aaron Rodgers, the reigning NFL MVP who is off to a historically strong start.

Rodgers, who ranks first in NFL history in passer rating (106.8), has become the second quarterback to throw 10 touchdown passes and no interceptions in his first three games. This week, Packers backup quarterback Scott Tolzien likened watching Rodgers to seeing Michael Jordan in his prime.

“He just keeps getting better,” Packers coach Mike McCarthy said. “I don’t know how much better he can play, frankly. But you never know with Aaron.”

And in this corner, we have the 49ers’ defense, which, frankly, has not invoked Jordan comparisons. In the past two weeks, the 49ers have been outscored 90-25, thanks partly to a secondary that has allowed the most completions of 20-plus yards (15) and 40-plus yards (five) in the NFL.

This week, the 49ers have discussed tightening the zone coverage that was picked apart for 676 yards and five touchdowns by Pittsburgh’s Ben Roethlisberger and Arizona’s Carson Palmer in the past two games.

“That’s kind of the downside of the zone,” safety Eric Reid said. “You’re not close to people. But we’ve got to do a better job of breaking on the throw.”

Yes, it doesn’t sound as if it will be a fair fight when the Packers (3-0) visit the 49ers (1-2) at Levi’s Stadium on Sunday. Just ask the oddsmakers: The 49ers are eight-point home underdogs for the first time since Dec. 15, 2007, when they were 8½-point underdogs against the Bengals on the way to a 5-11 season.

Safety Antoine Bethea understands many are forecasting an early round knockout.

Aaron Rodgers has 10 touchdowns through three games and faces a 49ers’ defense that has struggled against the pass. Aaron Rodgers has 10 touchdowns through three games and faces a 49ers’ defense that has struggled against the pass. Photo: Christian Petersen, Getty Images Photo: Christian Petersen, Getty Images Image 1 of / 1 Caption Close Will Aaron Rodgers feast on 49ers’ defense? 1 / 1 Back to Gallery

“The outside — they’re going to say what they say,” Bethea said. “They call it any given Sunday for a reason. So we’ve got to go out there and we’ve got to play.”

The 49ers have played well against Rodgers in recent years. Rodgers is winless in his past four starts against the 49ers, a stretch that includes two postseason games. The 49ers haven’t exactly stopped him — he has averaged 268 yards, two touchdowns and had a 96.0 passer rating — but he has looked just good, not Jordan-like.

“He’s playing well,” inside linebacker NaVorro Bowman said. “But we’ve had great success against him in the past. And hopefully that carries over to Sunday.”

What’s been the 49ers’ secret? Bowman referenced the ability to rough up Rodgers: They had 10 sacks and 19 quarterback hits in the past four meetings.

“We got pressure on him,” Bowman said. “We kept him in the pocket. You do those things and you have a great chance to win against Aaron Rodgers.”

There is, of course, a problem with drawing too much from this recent history: Many of the defenders who have helped harass Rodgers are history.

Rodgers will survey a defense Sunday that includes just one starter — outside linebacker Ahmad Brooks — with more than 10 career sacks. The 49ers have had one sack and three quarterback hits the past two weeks from a defense that includes untested starters in defensive tackle Quinton Dial (nine career starts), outside linebacker Aaron Lynch (five) and cornerback Kenneth Acker (three).

Rodgers said it will be a bit strange to not see familiar faces such as Aldon Smith, Patrick Willis, Justin Smith and Ray McDonald.

“I enjoyed the challenge of playing against those guys,” Rodgers said. “They’re great players. I always enjoyed competing against them. It will be different, but they still have guys with that name recognition and young guys who are trying to make a name for themselves.

“So that’s what happens in this league. There’s a lot of turnover. There’s a lot of changes over the years. It’s a young man’s game. You have to kind of fight against Father Time to hold on.”

Rodgers, who will turn 32 in December, is clearly dominating that battle as he prepares for what could be a one-sided fight Sunday.

“We’re all witnessing something special,” Packers wide receiver James Jones said to Green Bay reporters. “We may not realize it until he’s done and retired how great he was.”

Davis unlikely to play: Tight end Vernon Davis is doubtful for Sunday. Davis did not practice this week because of a knee injury that sidelined him in last week’s loss at Arizona. The 49ers listed nine players as probable.

Eric Branch is a San Francisco Chronicle staff writer. E-mail: ebranch@sfchronicle.com Twitter: @Eric_Branch

Nearly perfect

Aaron Rodgers’ stats through three games:

Completions64

Attempts91

Comp pct. 73.6

Yards771

Touchdowns10

Interceptions0

QB rating135.4

Far from perfect

The 49ers’ pass defense through three games (NFL rank among 32 teams):

Comp pct. 70.3 (28)

Yards853 (26)

Yds/attempt10.0 (32)

Touchdowns5 (T12)

Interceptions2 (T17)

Sacks6 (T12)

QB rating111.6 (30)