GLENDALE, Ariz. -- On Tuesday, San Francisco 49ers quarterback Jimmy Garoppolo was asked if he was OK with not getting much of the attention for his team's unblemished start.

Garoppolo smiled, shrugged his shoulders and replied, "I'm all right with being undefeated, yeah."

Two days later, Garoppolo found himself in the middle of the Niners' locker room being showered by his teammates with chants of, "JIM-MY, JIM-MY, JIM-MY" after helping the Niners not only remain unbeaten by virtue of their 28-25 win against the Arizona Cardinals, but also silence, at least for one night, those questioning whether he could carry the freight when the defense and running game aren't firing on all cylinders.

Not that Garoppolo was too concerned about the outside questions.

"It doesn't bother me," Garoppolo said. "Most of the people saying the stuff are just people, so it's their opinion. You can't think too much about that stuff. It's not going to change who I am as a quarterback."

With the win, the Niners improved to 8-0 on the season for just the second time in franchise history -- joining the 1990 squad. They also joined the New England Patriots as the only unbeaten teams this season.

Garoppolo, who was traded to San Francisco from New England exactly two years ago on Halloween, put together perhaps the best start of his career to get the Niners there.

With the Cardinals loading the box to stop the run and having success, Shanahan put the game in Garoppolo's hands. Thursday's game was the first this season in which the Niners had more passing attempts (37) than rushing tries (31).

Garoppolo finished 28-of-37 for 317 yards with a career-high four touchdown passes, no interceptions and a passer rating of 136.9, also a career high.

"He played great today," coach Kyle Shanahan said. "He made a lot of plays in rhythm and made a lot of off-schedule plays. ... I thought Jimmy played a hell of a game. His best game yet, probably."

Just as important as the touchdowns, Garoppolo delivered on third down repeatedly, including on a pivotal final drive as the Niners put the pesky Cardinals away. He hit receiver Emmanuel Sanders for 16 yards on third-and-11 from Arizona's 25 and tight end Ross Dwelley for 11 yards on third-and-4 after scrambling out of danger to keep that drive going and end the game.

Garoppolo finished 12-of-14 for 159 yards and three touchdowns on third down. Nine of his 12 completions moved the chains or went for a touchdown.

"That's usually where quarterbacks earn their money," Shanahan said. "You can do a lot of things on first and second down. You can mix in run or pass to even out the game, but on third down, that pass rush is coming. They always have their best coverages and blitzes called. You need a good guy back there. Everyone knows how well he can throw, but he was on tonight throwing and he got to the right spots, and when it wasn't there, he made plays with his legs."

With the four touchdown throws in the first three quarters, Garoppolo became the first Niners quarterback to throw that many scores in the opening three quarters of a regular-season game since Jeff Garcia did it in 2003 against the Cardinals.

Garoppolo's fourth touchdown pass was one of his best throws of the night, dropping it perfectly over Arizona defenders in the corner of the end zone to wideout Dante Pettis for the score.

Although he still put together one of his best statistical performances, Garoppolo's stat line could have been even bigger were it not for drops such as receiver Deebo Samuel's in the end zone and another in the fourth quarter on a screen to running back Tevin Coleman that might have gone for a big gain.

Regardless, Garoppolo's effort was just enough to get the Niners to 8-0 as they survived their toughest test since Week 3. The victory puts them with the Patriots in some promising company. According to ESPN Stats & Information research, this is the fourth time in the Super Bowl era that multiple teams have started undefeated through eight games. In each of the previous three instances, at least one of those teams made the Super Bowl, and in 2009, both teams to do so -- the Saints and Colts -- met in the Super Bowl.

The win also bolstered Garoppolo's career record, moving it to 16-2 in 18 starts. Garoppolo is the fifth quarterback in NFL history to win at least 16 of his first 18 starts, according to the Elias Sports Bureau data. He joined Daryle Lamonica, Ben Roethlisberger, Dan Marino and Roger Staubach in that group. He's now 14-2 in his career with the Niners.

"He's pretty good," tight end George Kittle said. "I don't know why people don't think he is. He makes some pretty gutsy throws out there, doesn't he? Goodness gracious ... I can't say enough about how he brings us along. Whether it's on the sideline or in the huddle, you know the leadership that he has. The fire that he has, too, just kind of, he gets the people going. And just to see him make those plays, allow him to get those people off his back that say, "Hey, maybe he's not you know, what we think he is." Everyone in this building and in our locker room knows what he is. It's fun to see that."