Click photo to enlarge
The 49ers are looking for Justin Smith to pick up the defensive slack left by the departure of tackle Bryant Young.

SANTA CLARA

THE START OF what will be a very long season for the 49ers comes Sunday. Lose that game to the Arizona Cardinals at Candlestick, and there goes any inspiration for the ensuing 15 tilts.

So how do the 49ers win Sunday, and how do they get off to a start that'll be gauged as promising (but almost certainly will be deceiving en route to a 3-13 season)?

By sacking Kurt Warner. By forcing him to fumble. By (gulp) giving the ball back to the 49ers offense so that J.T. O'Sullivan can show off that 2007 NFL Europa form.

"Warner is definitely a guy you want to make move," new 49ers defensive savior Justin Smith said Monday. "He can pick you apart if he gets time. Getting pressure on him is a big key."

Whoa, time to back up here. Smith, a defensive savior? Look, he is the prize of the 49ers' latest offseason splurge in free agency (as cornerback Nate Clements was in 2007, wide receiver Antonio Bryant in 2006 and left-tackle-turned-right-tackle Jonas Jennings in 2005).

Unlike most players, Smith can't really be linked to one position, so "savior" works for now, at least until the 49ers show they can't be saved, yet again during the Mike Nolan regime.

Smith is more than a high-priced defensive end. He'll also line up at outside linebacker and at defensive tackle, making it unpredictable where his high-wire act unfolds.

"I like it," Smith said of his position juggling. "It gives me opportunities to move around and get on different guys."

This guy oozes energy. His gas tank is full, ready for the four-month drive ahead of him. The 49ers better use Smith to the max. He must help fill the void on defense created by Bryant Young's retirement.

This offseason has been so consumed with the 49ers' quarterback competition — a poorly handled one, by the way — that Young's departure from the defense has been overlooked, even though it can't be.

"It's a learning experience for us, and we've got to step up to fill that area, to take over the area B.Y. left," defensive end Isaac Sopoaga said. "Everything that has to deal with football, that's what we miss from B.Y."

That defense needs a new leader, as does the whole team. Is Smith (Justin, not Alex) up for the task?

"Leadership is going out and setting an example of how to play and prepare," Smith responded.

Now that he's escaped the WKRP-like circus in Cincinnati after seven years, Smith is eager to suit up for the 49ers, who've paid him $20 million guaranteed.

"You definitely always have something to prove," Smith said. "It's refreshing to come here. It almost feels like my rookie year again."

Food for thought: Smith put up 81/2 sacks as a fresh-faced, first-round draft pick in 2001. And here he gets Warner out of the gate? Heck, don't rule out 81/2 sacks this Sunday alone.

But seriously, a stronger pass rush is vital for the 49ers this year.

If their offense is indeed improved courtesy of Mike Martz's boost, then opposing teams won't just be running the ball to kill the clock and sit on a lead. Opponents might have to play catch-up more often, and the 49ers' defenders better be capable of harassing quarterbacks.

"It all depends on how the defensive line plays," backup defensive end Ray McDonald said. "Defensive line and quarterback, those are the most important positions."

Those certainly are on this team, primarily because of the unknown talents offered there.

McDonald looked good in the exhibition season, and he noted that he's feeling more comfortable and more savvy with his hands (courtesy of B.Y.'s tips, he said). Maybe the 49ers will get more from Tully Banta-Cain, who oddly had to play the final minutes of Friday's meaningless exhibition finale. Maybe linebacker Manny Lawson returns swiftly from his 2007 knee injury. Maybe Parys Haralson or Rod (or is it Roderick) Green will break out. Maybe there'll be crushing blitzes by defensive backs Clements, Shawntae Spencer and the underutilized Dashon Goldson. Maybe tackling machine Patrick Willis gets into the backfield, too.

What to expect of 2008 first-round pick Kentwan Balmer? "I don't know," Balmer replied. "We've got great talent up front with veteran guys. We'll see what happens."

We saw a great defensive line lead the New York Giants to last season's Super Bowl title. If we see a 49ers victory Sunday (official prediction comes Thursday), just remember they also beat the Cardinals to open last season's 5-11 campaign.

Contact Cam Inman at cinman@bayareanewsgroup.com.