SAN FRANCISCO (AP) – Against a struggling opponent with a rookie quarterback and a patchwork defense, Peyton Manning and the Indianapolis Colts were only as good as they needed to be.

Edgerrin James rushed for 105 yards and a touchdown, and the Colts intercepted four passes by No. 1 draft pick Alex Smith to remain unbeaten with a lackluster 28-3 victory over the San Francisco 49ers on Sunday.

While Smith’s struggles were predictable in his first career start, the Colts’ problems were surprising – but not a big deal. Manning went 23-of-31 for 255 yards and one score, throwing two interceptions in an unimpressive performance against a team starting two recent practice squad players in its secondary.

The reigning league MVP also failed to hook up with Marvin Harrison for the duo’s 86th touchdown, which would have broken the NFL record shared with San Francisco’s Steve Young and Jerry Rice.

But the Colts scored two fourth-quarter touchdowns on James’ 4-yard run and Troy Walters’ 18-yard reception to blow open a surprisingly close game. Cato June returned an interception 24 yards for a score in the second quarter, and Dominic Rhodes rushed for an early TD.

Indianapolis (5-0) still won easily because its inconsistencies were nothing compared to Smith’s troubles.

Smith, promoted to the starting lineup after a month of mediocrity from Tim Rattay, never got comfortable behind San Francisco’s terrible offensive line. Though the rookie didn’t seem intimidated by Indianapolis’ constant rush, he went 9-of-23 for 74 yards and committed five turnovers while getting sacked five times.

In its fourth straight loss, San Francisco (1-4) failed to score an offensive touchdown for the second straight game despite a rare impressive performance from Kevan Barlow, who rushed for 99 yards.

Smith’s headset apparently malfunctioned on the opening drive, and things never got much better. He had three interceptions, got sacked twice and fumbled once in the first half, with his quarterback rating dropping to 4.4 when Mike Doss intercepted his pass into triple coverage 1:04 before halftime.

Smith completed just one pass to a wide receiver all day, with Brandon Lloyd and Arnaz Battle getting completely shut out.

Smith made his first big mistake in the second quarter, misreading the Colts’ coverage and throwing straight to June, who scored the first touchdown of his NFL career.

The Colts drove 95 yards on their second possession, but James fumbled while attempting to stretch the ball over the goal line. Manning then got sacked for the first time all year when Andre Carter broke through the line 31/2 minutes before halftime.

Manning threw a terrible interception moments later, completely failing to see 49ers linebacker Derek Smith in coverage.

Trailing 14-0, the 49ers recovered Joe Nedney’s onside kick after halftime and sustained a solid 10-play drive for Nedney’s 30-yard field goal. The 49ers then tried another onside kick, with Nedney using his non-kicking foot this time – and the ball was available on the turf before the Colts recovered.

AP-ES-10-09-05 1923EDT

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