ATLANTA — San Diego's Philip Rivers led touchdown drives in two of his three possessions in his first game since signing a contract extension, before the Atlanta Falcons' backups rallied to beat the Chargers 27-24 in an exhibition game Saturday night.

The Chargers led 21-10 as the first-team offense ran smoothly even with LaDainian Tomlinson and Antonio Gates watching from the sideline.

Rivers completed 10 of 15 passes for 185 yards and a touchdown. He signed a six-year, $93 million extension Monday.

The Chargers frustrated the Falcons' defense with big third-down plays.

Darren Sproles, who started at running back for Tomlinson, scored on a 10-yard run to cap San Diego's opening drive. Rivers added a 48-yard screen pass for a touchdown to Michael Bennett.

Tomlinson and Gates participated in pregame warmups before the team announced they would not play.

Gates' status for the game had been uncertain. He missed three practices during the week with what he said was general soreness.

Tomlinson had 12 carries for 28 yards in the Chargers' first two preseason games. A Chargers spokesman said Tomlinson has no reported injury.

Falcons coach Mike Smith kept quarterback Matt Ryan, running back Michael Turner and most other offensive starters in the game for the first possession of the third quarter.

Ryan was 14 for 20 for 140 yards, including a 12-yard touchdown pass to Brian Finneran in the first quarter.

Chris Redman completed a 5-yard touchdown pass to Eric Weems with 9 seconds remaining to give the Falcons the win.

Redman, who took over for Ryan in the third quarter, completed 15 of 19 passes for 134 yards and the game-winning touchdown. Redman also ran for a score.

Redman's fourth-down pass to Weems capped an 11-play, 75-yard drive.

The Chargers were successful on 7 of 8 third-down plays in the first half, many for big yards.

Rivers completed third-down passes for 18, 32, 18 and 48 yards on the Chargers' second touchdown drive, including the 48-yard touchdown pass to Bennett on third-and-24.

The big third-down plays enabled San Diego to overcome 35 yards in penalties and a 10-yard sack by Falcons cornerback Brent Grimes on the drive.

The Chargers' third-down magic continued with Billy Volek at quarterback late in the first half. Volek's 22-yard pass to Buster Davis on third-and-22 helped set up his 10-yard touchdown pass to Malcom Floyd for a 21-10 lead.

Volek completed 7 of 9 passes for 102 yards and a touchdown.

Gartrell Johnson broke free on a 42-yard run late in the fourth quarter on yet another big third-down play for the Chargers.

Turner led Atlanta with 12 carries for 47 yards. Marty Booker had six catches for 62 yards.

NOTES: Brandon Manumaleuna started for Gates at tight end and had one catch for 9 yards. ... Falcons RB Jerious Norwood hurt his left knee in the first half and did not return. ... Rookie CB Chris Owens left with a knee injury late in the first half. ... Another Atlanta rookie, S William Moore, hurt his hamstring after missing the first two preseason games with a knee injury.