Alex Smith has plenty of work to do.

The first overall pick in April's draft, Smith struggled in his preseason debut as the San Francisco 49ers posted a 21-13 triumph over the Oakland Raiders .

The contest also marked the debuts of Niners coach Mike Nolan and star wide receiver Randy Moss , whom the Raiders acquired in an offseason trade from the Minnesota Vikings .

Trying to become the next great quarterback for a franchise that has produced Hall of Famers Joe Montana and Steve Young , Smith was given the starting assignment. He played the entire first half, failing to lead a scoring drive while completing 3-of-9 passes for just 25 yards.

Tim Rattay , who started nine games last season, took over in the third quarter and threw touchdown passes of 36 yards to Brandon Lloyd and 13 yards to Arnaz Battle . Rattay went 6-of-8 for 103 yards.

The Niners (1-0) had to be encouraged by sixth-round pick Derrick Johnson . The cornerback returned an interception 87 yards for a touchdown in the third quarter.

Moss was not much of a factor in his first game, catching one pass for 11 yards.

Sebastian Janikowski kicked field goals of 20 and 44 yards in the first half for the Raiders (0-1).

Oakland's Kerry Collins completed 8-of-12 passes for 68 yards. LaMont Jordan , the club's new running back, carried four times for 12 yards and added four receptions for 23 yards.