Kyle Shanahan was rightly worried the San Francisco 49ers left too much time on the clock for Aaron Rodgers in their thrilling defeat to the Green Bay Packers.

The Niners suffered their first defeat of the season in Week 3 as Mason Crosby's 51-yard field goal as time expired gave the Packers a 30-28 victory.

Thirty-seven seconds earlier, fullback Kyle Juszczyk had ploughed into the endzone to give a 49ers team that had trailed 17-0 a 28-27 lead on a 12-yard pass from Jimmy Garoppolo.

Despite having all three timeouts, Garoppolo snapped the ball with 12 seconds left on the play clock, meaning he had the chance to salt more of the clock away and diminish the odds of Rodgers leading a decisive drive.

Instead, Rodgers hit Davante Adams for receptions of 25 yards and 17 yards to set up Crosby to settle the game in Packers' favour.

Asked if he was worried about the amount of time left for the reigning MVP, San Francisco head coach Shanahan told a media conference: "You always worry with Aaron on the other side.

"That's why we didn't use any timeouts. We wanted to take it down. Hell of an effort by Juszczyk to get it in.

"I think [Garoppolo] hit the last guy in the progression and it was a hell of an effort after the catch."

Had Juszczyk been tackled short of the endzone instead of crossing the line with an extra effort, the Niners would have been able to use their timeouts to control the clock and potentially score while leaving the Packers with virtually no chance.

But curbing that instinct to score is near-impossible in the heat of the moment.

"I didn't really have a lot of time to think about it," Juszczyk said. "The entire team was swarming me. I didn't even know how much time was left on the clock to be totally honest with you.

"It wasn't really something that was on my mind during the play. We were down six so we needed a touchdown so I was trying to score."

"We were kind of in a good rhythm,” Garoppolo added. "That's when you tow the line of you have the defense on their heels, it's really hard to score down there in the red zone as it is, do you want to let them catch their breath? 

"When a guy catches it and makes a play like that you’re not going to be upset at him for scoring. It’s tough."