SANTA CLARA, Calif. -- Justin Smith may have lost a step or two since his All-America days at Missouri, but there's no denying his desire to compete at a high level in the NFL.
The five-time All-Pro defensive lineman is limited at San Francisco 49ers practice during the week but ready at game time. Smith, who turned 35 Tuesday, has recovered from last year's shoulder injury.
"Your eyes go to him as you're watching the game," San Francisco coach Jim Harbaugh said Friday. "There's just so much energy and aggressiveness, the way he plays the game. He always looks good to me."
After four games, Smith is on pace for 12 sacks and 100 tackles.
"I can use my left arm this year -- that's a plus," Smith said. "I feel good enough with where I'm at and what I'm doing. Let's keep on trucking."
Smith helps keep the 49ers defensive front running smoothly, which often means a choppy road for running backs. San Francisco ranks second in rushing defense, first in the NFC, heading into Sunday's game against Kansas City.
"We just go out, try to compete and do what we do as a unit," Smith said. "There are a lot of great running backs and a lot of great lines. We have another big challenge in front of us."
Without Aldon Smith in the lineup -- he has five games remaining on his suspension -- Justin has managed to keep things together as much with his brain as with his brawn.
"Ian (Williams) is playing well. Glenn (Dorsey) is playing well," Smith said. "Teams have been trying to run right at Ian, but he's strong at the point and fast at pass rushing. You can always pass rush better. Week in and week out, you look to take advantage of the protection we're getting."
Smith left Missouri after setting single-season school records for sacks (11) and tackles for a loss (24). As a rookie with the Cincinnati Bengals in 2001, he recorded 8 1-2 sacks, a career high he matched in 2010 with the 49ers.
He's currently ranked eighth among active sacks leaders, although numbers can't totally measure his value. He's also a leader on the field and in the locker room. Teammates say he talks to everybody and lightens up tense moments.
"If I can get warmed up and moving around," he said, "I feel fine."
NOTES: OL Jonathan Martin, who also played for Harbaugh at Stanford, was asked about Deion Sanders' latest comments about the "rift" in the 49ers locker room. "My reality, day to day, is that this is one of the strongest locker rooms I've been around," he said. .TE Vernon Davis said there's "a small chance" he will be able to play Sunday, though he did not practice Friday. He's listed as questionable along with CB Tramaine Brock (toe), T Anthony Davis (knee) TE Vance McDonald (knee), S Eric Reid (hamstring) and NT Ian Williams (ankle). . C Marcus Martin (knee) is doubtful, while S Antoine Bethea (ankle), WR Michael Crabtree (foot), RB Frank Gore (back), DE Tony Jerod-Eddie (shoulder) and P Andy Lee (ankle) are probable.