San Francisco 49ers bench struggling Jimmy Garoppolo for C.J. Beathard vs. Miami Dolphins

SANTA CLARA, Calif. -- San Francisco 49ers quarterback Jimmy Garoppolo's return from a high right ankle sprain lasted only a half-game Sunday against the Miami Dolphins.

Garoppolo started after a two-week absence caused by the injury he suffered in a Week 2 win against the New York Jets. But he and the rest of the Niners struggled mightily, falling behind 30-7 in the first half against the Dolphins. Those struggles prompted coach Kyle Shanahan to turn to backup C.J. Beathard to start the third quarter.

Asked what went into that decision after the Niners' 43-17 loss, Shanahan indicated it was a little bit of everything and that he wanted to protect Garoppolo from further injury.

"Just the way the whole game was going," Shanahan said. "Just kind of watching how we were playing as a whole, how he was playing. You could tell he was affected by his ankle. ... But I know he doesn't normally throw the ball that way, and I think he was struggling a little bit because of it and the way the game was going, that I wasn't going to keep putting him in those positions knowing we were going to have to throw it a lot to come back."

Garoppolo was under pressure for much of the first half as the Dolphins sacked him three times and had four quarterback hits. He threw two second-quarter interceptions as he struggled to get comfortable in the pocket.

In his two quarters, Garoppolo was 7-of-17 for 77 yards with no touchdowns and the two interceptions for a career-low passer rating of 15.7. Garoppolo was just 1-of-4 with the two interceptions on passes traveling 15 or more yards downfield, and he was 1-of-6 for 20 yards with an interception when the Dolphins blitzed, according to ESPN Stats & Information research.

After the loss, Garoppolo said he felt the injured ankle, particularly when he was trying to push off and drive the ball downfield. Despite his struggles, Garoppolo said he wanted to finish the game before Shanahan decided to go with Beathard.

"I wanted to be out there," Garoppolo said. "I'm the quarterback of this team and it's my job to be out there and put the team in position to be successful. Kyle made the decision at halftime. He's the head coach so I followed it. It was just tough. I want to be out there with my guys battling, whatever the situation is."

Moving forward, Garoppolo said his confidence is unshaken by Sunday's outing but he was unsure of his status for next week's game against the Los Angeles Rams.

"I really haven't thought that far ahead," Garoppolo said. "I guess we'll just take it day by day with the ankle and see how it goes."

Beathard made his second relief appearance in as many weeks. He stepped in for Nick Mullens in last week's loss to the Philadelphia Eagles and almost led the 49ers to a comeback victory.

After that performance, Shanahan promoted Beathard to the No. 2 quarterback spot this week with Garoppolo reclaiming the starting job. During the week of practice, Garoppolo, Beathard and Mullens all got reps, with Garoppolo practicing on a limited basis on Wednesday and Thursday before taking on a full workload Friday.

Although there were some questions about his availability this week, Garoppolo said he told himself this past week he'd be ready to play the Dolphins and that the ankle felt good on Sunday.

Beathard didn't fare much better than Garoppolo in the second half. He led a touchdown drive that was capped by a 19-yard scoring toss to receiver Kendrick Bourne, but the offense struggled to get much of anything else going.

In his two quarters, Beathard was 9-of-18 for 94 yards with the score for a passer rating of 84.0, and the Niners never got into rhythm on either side of the ball.

"We haven't been playing very good complementary football, offensively and defensively, whereas last year when our defense would step up big, we'd get the ball and go down and score," Beathard said. "Right now, we're kind of struggling with that ... We saw that today. It stuck out."