SANTA CLARA, Calif. — Joe Staley got a good portion of his NFL education at Giants Stadium last season, but the guy who gave those lessons to him won't be around Sunday to see how far the San Francisco left tackle has progressed.

As a rookie right tackle last October, Staley yielded 3› sacks to Michael Strahan and his teammates in the 49ers' loss to the New York Giants. Staley started every game at right tackle last season before switching sides on the line this fall, but that trip to New Jersey taught him more about what not to do than any of the other 15 games.

Strahan's mere presence affected the mental preparation for a small-town Michigan kid thrust into the New York spotlight, and Strahan capitalized with an array of veteran moves.

"I wasn't in the right frame of mind," Staley said Wednesday. "I was thinking, 'Oh my God, I'm going against Michael Strahan.' ... You can't just react (to an opponent). You have to be the aggressor. You have to have a game plan going in, and you can't be reactive. I didn't do that."

When the Giants lost Osi Umenyiora to a season-ending injury in the first game of this season, Staley joined most Giants fans in hoping Strahan would come out of retirement — even though Strahan would have been mostly blocked by Barry Sims, the new right tackle.

"I was actually hoping to get a rematch," Staley said. "I know I wouldn't do what I did last year. I learned from it and moved on."

Offensive coordinator Mike Martz has received more credit than the 49ers' offensive line for running back Frank Gore's outstanding start to the season, but the NFL's leader in total yards from scrimmage knows he's getting help from the reconfigured group. Staley and center Eric Heitmann are the line's leaders, particularly while popular veteran right tackle Jonas Jennings struggles to recover from yet another injury.

"Those guys are one of the best lines, but they don't get any credit," said Gore, who has 720 yards from scrimmage through six games — including 524 on the ground, fourth-best in the league. "They're getting better as the season goes on, too. They're the reason we're being so successful in the running game."

Coach Mike Nolan believes Staley in settling in well to the everyday demands of being a left tackle. After a rough performance in the 49ers' first game against Arizona, Staley appears to be getting better at the minor details that make a major difference for offensive linemen.

"I feel like I'm getting better every game," Staley said. "The first game I didn't play very well, and I was very upset with myself. Going forward, I feel like I'm making progress as far as my technique goes. There are always things you can work on."

NEW FULLBACK: The 49ers signed fullback David Kirtman on Wednesday to replace Zak Keasey, who's out for the season with an arm injury.

Kirtman, who blocked for Reggie Bush and LenDale White during college at Southern California, was on the San Diego Chargers' practice squad for the past six games after Seattle released him. He spent his first two NFL seasons with the Seahawks, playing in six games last year.

The 49ers placed Keasey on injured reserve Tuesday after the fourth-year pro tore the biceps tendon on his right arm during special-teams play in last Sunday's 40-26 loss to Philadelphia.

The 49ers chose Kirtman to fill the roster spot largely because he's already familiar with their offense's terminology from his time with the Chargers, who use the same verbiage.

If Kirtman isn't ready to play when San Francisco (2-4) visits the New York Giants on Sunday, coach Mike Nolan said special-teams standout Michael Robinson and tight ends Delanie Walker and Billy Bajema will fill in at fullback.

EXTRA POINTS: S Mark Roman didn't practice Wednesday because of a minor knee injury, but it isn't expected to sideline him for Sunday. ... LT Jonas Jennings (shoulder) still isn't expected back this week, but LB Manny Lawson (hamstring) might be ready to return after participating in practice. ... CB Walt Harris and RB Frank Gore also sat out of practice to rest, while CB Donald Strickland (hip) was limited. ... The 49ers still haven't placed CB Shawntae Spencer on injured reserve, three weeks after he underwent season-ending surgery to repair a torn ligament in his left knee. Coach Mike Nolan says the 49ers don't feel the need to make a move until they find somebody who can contribute to their 45-man active roster on game days. San Francisco also saves money each week it doesn't have a full roster. ... Nolan usually holds practice at 10 a.m. during weeks when the 49ers must play an East Coast game starting at that early hour, but he used a normal schedule this week, saying the coaches couldn't get all their work done in time to prepare for practice.