SANTA CLARA – Jim Harbaugh spoke about Justin Smith on Monday as if a beam of light had hit the 49ers defensive end's helmet before his critical end-of-game play a day earlier.

"Justin's walking out onto the field," Harbaugh said, recounting a scene in the fourth quarter Sunday against quarterback Eli Manning and the Giants in which Smith was talking to fellow defensive end Ray McDonald. "He's telling Ray, 'Ray, be conscious of the B gap. Stay in your lane. Take away the B gap. Keep your hands up. He's going to throw it in the B gap.' …

"And sure enough, Eli sets up, and he was trying to hit the little short post throw right through the B gap. And there is Justin to knock it down."

The batted pass that preserved the 49ers' victory wasn't because of Smith's clairvoyance; instead, as Harbaugh said later, it was an example of the veteran's perception and instinct.

That has been a common theme for the 49ers, whose defense is 11th in the league in yards allowed per game but is first in fewest points allowed (15.3 per game). And Sunday's game was an excellent example.

Manning and the Giants had 395 yards and moved the ball inside the 49ers' 15-yard line four times, but those opportunities yielded only 13 points. The Giants scored one touchdown, twice were held to short field goals and turned the ball over on downs after Smith's batted pass.

The 49ers also intercepted Manning twice, and they lead the league in takeaways (21) and turnover ratio (plus 13).

"Turnovers are huge," outside linebacker Parys Haralson said. "If you get a lot of turnovers, you're giving the offense more time to score. That's what we've basically been doing – creating turnovers, putting pressure on the quarterback. All of that works together."

Cornerback Carlos Rogers had both interceptions, and he's tied for the league lead with five.

In the second quarter, Rogers was nearly burned by Giants wide receiver Victor Cruz, who dropped a deep pass along the sideline. Rogers said he was surprised when Cruz ran the same route on the next play and Manning threw the same pass.

This time, Rogers pressed Cruz at the line of scrimmage, then guessed correctly that Cruz again would turn the route to the outside.

"If he had run something else, he had me," Rogers said Monday.

On the second interception, Rogers suspected Mario Manningham was running a route across the middle. Instead, Manningham broke off his route, but Manning already had thrown the ball, and Rogers was in perfect position for his second interception.

Again, Rogers said if his intuition had been wrong, it would have resulted in a big play for the Giants.

"You can't go in afraid to make a mistake," Rogers said. "If you make a mistake, the game isn't over. That's my mindset throughout the game: At the end of the day, it's a big game and a big stage. But it's still football. You can't come in scared to make a mistake."

Said Harbaugh of Rogers: "He's got a very good feel, he's a veteran player, and that's what I tell him. … We want him playing within the framework of the defense first and foremost, but when there's evidence that you can make a play and a player feels like they can take a risk and make a gamble, then they have that freedom to do it, too."

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