Analysis: 49ers' turnaround has happened quickly

SANTA CLARA - Two years to the day that Jimmy Garoppolo arrived in San Francisco to join an 0-8 team, he played perhaps his best game with the 49ers to improve the team to 8-0.

It's been quite a remarkable turnaround in coach Kyle Shanahan's third year.

With Garoppolo stabilizing the quarterback position and showing signs of brilliance like in the 28-25 win at Arizona on Thursday night, a defense fortified by edge rushers Nick Bosa and Dee Ford and Shanahan's play-calling that creates mismatches all over the field, the Niners (8-0) are a Super Bowl contender at the halfway point of the season after five years of struggles.

But they know there's plenty of more work to do.

“Eight and 0 is not going to get you anything, but it's a good start,” Garoppolo said. “We'll take the weekend to heal up, get some guys back and make a run at this thing. I think we've got a good group here. We've got a long way to go, but we're on the right track.”

The 49ers have been one of the NFL's biggest surprises in the first half, joining defending champion New England as the league's only unbeaten teams after winning just 17 games the previous four years, including 10 under Shanahan the past two seasons.

But he was putting a foundation in place during those years, most notably with the addition of Garoppolo, and that is paying dividends now. Shanahan has joined Tom Landry and Marvin Lewis as the third coach to start a season 8-0 for a franchise after previously losing the first eight games of the season.

Key number

8-0. There have been 14 teams that started a season 8-0 before this year under the current eight-division format that began in 2002. Those teams averaged 13 wins and all made the playoffs with the Colts (2006) and Saints (2009) winning the Super Bowl.

What's working

When you start the season 8-0, almost everything is going well. The strength of the team is a defensive line filled with first-round picks that is putting relentless pressure on the quarterback and a powerful running game led by Matt Breida and Tevin Coleman.

What needs help

Run defense. One of the few holes in the team so far has been a run defense that has been gashed the past two weeks by Christian McCaffrey and Kenyan Drake. San Francisco had a few issues earlier in the year shutting down the run as well, but it hasn't been a major issue yet because the Niners have been playing with the lead for most of the year, often forcing the opposition to pass.

Stock up

Garoppolo. Garoppolo had played fairly well the first seven games but wasn't needed to carry the team thanks to the running game and defense. But with the run game stopped Thursday and the defense tired on a short week, Garoppolo delivered his best game yet. He went 28 for 37 for 317 yards and threw four touchdowns.

Stock down

CB Emmanuel Moseley. Moseley had been outstanding since stepping in for the injured Ahkello Witherspoon, allowing just five catches on 15 targets for 40 yards in his first four games. But he wasn't as effective against the Cardinals and made a bad read on a pass that led to an 88-yard touchdown.