Alex Smith had three receivers lined up to his left and one to his right.

But when the 49ers quarterback was confronted with an Eagles blitz on a key third-quarter third down Sunday, he ran to the wrong side, which was his right.

It wasn't as if Smith made an incorrect choice all on his own, although he had made plenty of them to that point. The Eagles - linebacker Tracy White, in particular - played a significant role in Smith's failing to convert another third down.

When White blitzed up the middle and got through unblocked, Smith had already curled to his right. But the linebacker wisely continued to shade the quarterback in that direction, and the largely immobile Smith had no choice but to scramble to his right and eventually heave the football out of bounds.

"We were able to get some pressure on the quarterback and, at times, move that pocket, and that becomes tough," coach Andy Reid said yesterday, a day after the Eagles handled the 49ers, 27-13. "That's a tough thing on a quarterback, when you put him into a full run."

It was all part of the plan for a Sean McDermott-coached defense looking to rebound a week after allowing 512 yards and 38 points to the New York Giants. The improved tackling and four turnovers were keys, but the statistic that demonstrated the unit's success was San Francisco's 0-for-11 conversion rate on third down.

The Eagles' defense has allowed just 32.6 percent of third downs to be converted, the best mark in the NFL.

"I thought we were awesome on third downs," Reid said. "Any time you can throw a no-hitter there on third down, that's a plus."

The Eagles were good on first and second down, too, leaving San Francisco with an average of 9.2 yards to go on third down. And with Smith placed into so many third-and-long situations, McDermott could unleash the blitz packages the quarterback called "unique" and "unconventional."

White's hurry of Smith - although he wasn't credited with one - was crucial because the 49ers had trimmed the Eagles' lead to 20-13 on their previous drive. And then, after forcing a punt, San Francisco sent a chill into an already freezing Lincoln Financial Field when running back Frank Gore broke loose for a 37-yard run.

The 49ers, now at the Eagles' 43, went right back to Gore, who forged ahead for 16 yards. But guard Chilo Rachal was called for holding Moise Fokou. Rachal, though, appeared to have squared up the rookie linebacker.

The penalty accounted for a 4-yard loss. Faced with first and 14, the 49ers made a peculiar call when they handed off to the rarely used Michael Robinson. Defensive tackle Mike Patterson split the double-team block of Rachal and center Eric Heitmann and dropped the former Penn State player for a 1-yard loss.

On second down, Smith hit receiver Michael Crabtree on a short crossing route. When the rookie turned upfield, Will Witherspoon was bearing down. Last week, Witherspoon was one of several Eagles defenders to miss in a similar situation. On this occasion, the linebacker almost was beat but grabbed Crabtree's thigh and brought him down after a 7-yard gain.

That set up third and 8. The Eagles were in their nickel package, as they had been for much of the game. Joselio Hanson, the fifth defensive back, blitzed from the right but was picked up by Gore. Smith should have thrown in Hanson's direction - he had three options there, after all - but White was already in his face.

White, who had an interception earlier in the game, shot through untouched because San Francisco's blocking became discombobulated. Rachal and Heitmann could have picked up White, but both appeared to focus on defenders - Witherspoon and end Jason Babin - who dropped back into coverage instead of rushing the passer.

Smith didn't make the right reads, either.

"Their defense does a lot of things quarterbacks aren't used to seeing," he said.

White, a special-teams standout whose defensive snaps have increased, forced Smith out of his comfort zone.

"We brought him here as a special-teams player, and Tracy told me when he got here, 'You know, I can play linebacker, too, if you give me a chance,' " Reid said.

White helped force a punt, the Eagles uncorked a long scoring drive, and Smith didn't have the right stuff to lead the 49ers to a comeback victory.

Contact staff writer Jeff McLane at 215-854-4745 or jmclane@phillynews.com.