SANTA CLARA — His coach says bad things happen when Alex Smith "presses."

Now, the 49ers' embattled quarterback will have to pull off quite a trick: Making good things happen when the pressure on him has never been greater.

One week after narrowly avoiding a benching, Smith will be playing to retain his starting spot and to help save the Niners' fast-crumbling season when San Francisco (0-5) hosts the Raiders (2-3) today at Candlestick Park. All this seven days after 49ers coach Mike Singletary gave him a sideline tongue lashing and nearly inserted backup David Carr, a dust-up that only increased the already intense level of scrutiny on the sixth-year quarterback.

Hey, no pressure, Alex.

"I just feel that at some point in time, not only do I realize it, but he realized that you know what, I've got to play my game," Singletary said. "I've got to be who I am. And go out there and get it done. And I believe that's what he's going to do."

The most important thing Smith can do is limit his turnovers. It can be reasonably argued that Smith, who has thrown an NFL-high nine interceptions, has been the primary reason the Niners are 0-5 instead of 3-2. In three losses by a combined eight points, Smith has committed seven turnovers — all in opponents' territory — including four inside the 36-yard line.

Safe to say, the Raiders' defense wants to follow the blueprint: Harass Smith and accept the resulting charity.

"Hopefully we can put some pressure on Alex Smith," Oakland defensive tackle Tommy Kelly told the San Francisco Chronicle. "He's had a little trouble throwing it to the other team this year."

Smith, who ranks 27th in the NFL with a 71.6 passer rating, has his own blueprint for improving on his mistake-filled performances — playing more fearlessly and taking more chances downfield.

On the surface, it sounds like a recipe for more disaster. But Smith has been at his best this season in San Francisco's two-minute offense — situations in which he's been forced to let it rip.

In last week's 27-24 loss to Philadelphia, for example, Smith sparkled in the final two minutes of the first half and in game's last 11 minutes. On those five hurry-up drives, Smith completed 18 of 24 passes for 193 yards with two touchdowns and one interception. On San Francisco's other eight drives, Smith was 7 of 15 for 116 yards with one touchdown and one interception.

Smith understands his vow to play 60 minutes in attack mode won't mean much if he doesn't deliver today.

"It's just a matter of making that commitment and not just saying it," Smith said. "It's a commitment you can't just talk about. It's a commitment you have to make within yourself, each and every one of us deep down in that you're going to change ... you're going to be different."

Much of the focus will be on Smith, but Oakland quarterback Jason Campbell, the season-opening starter, also has something to prove. With Bruce Gradkowski (shoulder) injured, Campbell will get another opportunity to prove his abysmal early season performance was an aberration.

Campbell, who was benched during a 16-14 win over the Rams in Week 2, filled in for the banged-up Gradkowski last week and completed 13 of 18 passes for 159 yards with a touchdown and no interceptions in a 35-27 upset win over the Chargers.

Campbell doesn't have fond memories of the 49ers. In San Francisco's 28-24 preseason win, Niners linebacker Travis LaBoy sacked Campbell, who was carted off the field with a shoulder stinger. Campbell has said the lingering effects from the injury contributed to his 57.7 passer rating in the season's first two weeks.

With a combined record of 2-8, both teams need a victory.

But the Niners are likely in must-win territory. No team in NFL history has ever started 0-5 and made the playoffs. Their postseason chances are already slim — at 0-6 they become microscopic.

If San Francisco can pull out the season's first win, however, their outlook could quickly become significantly brighter. Their next three opponents — the Panthers, Broncos and Rams — have losing records and own a combined mark of 4-11.

But Singletary is hardly looking ahead. Better than most coaches, he knows how difficult just getting one victory can be.

"We all know," he said, "that the bottom line is we need to win."

For more on the 49ers, go to Instant 49ers at blog.pressdemocrat.com/49ers. You can reach Staff Writer Eric Branch at eric.branch@pressdemocrat.com and follow him at twitter.com/Eric_Branch.