SAN FRANCISCO (Ticker) -- With the core of the offense skipping the final exhibition game, the rest of the San Francisco 49ers showed how eager they are to contribute.
On San Francisco's first possession, Rattay organized a 12-play, 69-yard drive capped by his two-yard dive into the end zone.
San Diego (2-2) was pinned on its 3-yard line after a downed punt, and second-year quarterback Drew Brees fumbled, positioning Rattay for a three-yard TD toss to James Jordan for a 14-0 lead.
Rattay started for Jeff Garcia and played the entire first half, completing 16-of-21 passes for 158 yards.
Reserve running back Jamal Robertson widened the lead with an 11-yard touchdown run that opened a 21-3 advantage in the second quarter.
San Diego scored its only points in the second quarter on a 39-yard field goal by Steve Christie.
It was the third game in 10 days for the 49ers (2-3), who have eight days until they open the NFL season on the road against the New York Giants next Thursday. The Chargers visit the Cincinnati Bengals on September 8.
Garcia and fellow Pro Bowler Terrell Owens did not see any action for the 49ers.
Brees, who last week was named San Diego's starter, played most of the first half before being replaced by Doug Flutie. He was 3-of-5 and finished the preseason without a touchdown pass.
Chargers running back LaDainian Tomlinson played for the first time in the preseason started and rushed four times for 19 yards. A 1,200-yard rusher as a rookie, he had been sidelined with a sprained left ankle.