DENVER -- Linebacker Parys Haralson dashed into the Denver Broncos backfield and put a fierce hit into quarterback Peyton Manning's torso.
It was too late.
Manning had just uncorked a pass, and it resulted in a 38-yard completion against a 49ers defense that hasn't looked its menacing self through three exhibitions.
"It's been a scary start," linebacker Ahmad Brooks said after the 49ers rallied for a 29-24 win Sunday. "But we're not really game-planning or watching too much film."
Added coach Jim Harbaugh: "We gave up some easy yards and found ourselves in not good position when it came to making tackles. Fundamental-type things are what we need to look at."
Manning looked every bit a four-time league MVP, showing no signs of the multiple neck surgeries that sidelined him last year in his Indianapolis Colts finale.
In the midst of completing his final eight attempts, Manning absorbed that lick from Haralson. Immediately, Manning pounced up and motioned with his finger for the Broncos to hurry down field for the next snap, deep in 49ers territory.
Asked if it's ridiculous for anyone to question his post-surgery ability, Manning simply responded: "Yes."
Haralson's hit was the physical test Manning couldn't exactly replicate March 13, when he worked out as a free agent for Harbaugh and offensive coordinator Greg Roman.
Manning completed 10 of 12 passes for 122 yards and engineered three scoring drives, the final
"He knew what we were going to do before the snap," Brooks said.
Added 49ers tight end Vernon Davis: "Peyton Manning was connecting with his receivers and doing a great job. Alex (Smith) was saying, 'We've got to go. Yeah, it's preseason but we've got to make a statement.' "
Down 17-0, the 49ers finally counterpunched when Smith found Davis down the left sideline for a 44-yard touchdown completion. That play came one snap after a failed Broncos onside kick.
The 49ers offense floundered at the start. Smith ran into a third-down sack on the first series, and he fumbled away Jonathan Goodwin's snap on the second possession; Smith hadn't committed a turnover since a Thanksgiving interception.
Smith opened his fifth and final series by launching a 50-yard, play-action bomb to Randy Moss, the 49ers' long-awaited deep threat. But Smith overthrew Moss and the three Broncos defenders covering him.
"You almost need to do that (deep pass) for effect, just to get defenses thinking about him," said Smith (5 of 7, 69 yards).
The 49ers attempted only 16 passes among their four quarterbacks. Colin Kaepernick further entrenched himself as the No. 2 quarterback, completing all four of his official passes for 80 yards after penalties nullified two earlier incompletions. Kaepernick's best play: nimbly eluding a sack and finding tight end Konrad Reuland for a 16-yard completion.
The race for the No. 3 quarterback job between Scott Tolzien and Josh Johnson stalled, and Harbaugh said, "I'm not ready to make that call yet." Tolzien was 1 of 4 for 16 yards and fumbled on a 2-yard scramble. Johnson overthrew his only pass to an open Garrett Celek inside the Broncos' 10-yard line.
Outside of roster battles, the 49ers face a bigger question: Will their defense be ready for the Green Bay Packers on Sept. 9?
Through three exhibitions, the first-string hasn't produced a sack or turnover. Three snaps into Sunday's game, the 49ers allowed Willis McGahee to run almost untouched 12 yards up the middle.
The 49ers defense, however, hasn't played all its usual starters together yet. Outside linebacker Aldon Smith (hip) and inside linebacker NaVorro Bowman (knee) sat out this exhibition despite warming up in uniform pregame. Those absences followed Aldon Smith's and Brooks' last weekend in Houston, and Justin Smith's night off in the opener.
"There hasn't been all the guys out there together at one point," Harbaugh said. "It's something we have to overcome, though. No excuses. And we'll keep striving to get better."
Two promising reserves did fare well for the 49ers defense: cornerback Perrish Cox and lineman Will Tukuafu.
In his return to Denver where he played as a 2010 rookie, Cox recorded his -- and the 49ers' -- second interception this preseason. Tukuafu recorded a fumble-forcing sack and also moonlighted at fullback to help spring Anthony Dixon for a 26-yard touchdown run.
San Diego (3-0) at 49ers (2-1), 7 p.m. KBCW