INDIANAPOLIS — Alex Smith has been stealing the headlines in San Francisco all week.

He's back as 49ers starting quarterback and getting help from the recently signed Michael Crabtree and the rejuvenated Vernon Davis. It looks like a whole new offense.

The unbeaten Colts aren't buying it.

"I don't think they're going to change their game plan just because he (Smith) is in there," cornerback Kelvin Hayden said. "I think they're going to try to get (Frank Gore) the ball."

If the 49ers make their expected power play, Indianapolis (6-0) will be in for a real challenge.

While three-time MVP Peyton Manning has gotten much of the credit for Indy taking another perfect mark into November, the fourth time in five years, it's the Colts' defense that has made the starkest improvements. The pass defense Smith faces is ranked No. 6 in the NFL even with rookie Jerraud Powers starting five games and undrafted rookie Jacob Lacey playing a prominent role since Week 2.

But the run defense remains a work in progress.

Indy is allowing 4.3 yards per carry, though it has played four of the league's top nine rushers. Gore is next in line, and he has something to prove after returning from an ankle injury and producing just 32 yards rushing last week at Houston.

So with a new quarterback and a preference for power over finesse, why would the 49ers (3-3) change?

"I would think the way Mike (Singletary) likes to play the game, they would be more of a run-oriented team," Colts coach Jim Caldwell said. "But they can spread it out and mix it up a little bit."

Actually, Singletary is seeking more balance in his offense. The hope is Smith will provide that.

The top pick in the 2005 draft won back his starting job after throwing three TD passes in the second half, all to Davis, in relief of Shaun Hill. It will be Smith's first start since Nov. 12, 2007, and coincidentally, it comes against the same team Smith faced in his first NFL start.

Singletary, the 49ers coach, is cautious about what should be expected.

"It's not that you just look at the quarterback position and go, 'Hey, yeah, we got a quarterback, so let's go,'" he said. "It is looking at the entire team, some of the things that we have done, some of the things we've been able to do, some of the things we haven't done very well. I just think we have to give ourselves a chance to get out there and play the game and play it as best as we can."

That won't be easy against Indy, which continues to meet its high standards.