It was a normal sensation for the 26-year-old, who always feels a wave of nervousness before he plays.
"I think if you don't (feel nervous), you're playing for the wrong reasons," Garoppolo said.
After Garoppolo engineered a fourth-quarter drive to set up a 15-14 comeback win over the Chicago Bears, it appears as if San Francisco has found the right quarterback. He completed 26 of 37 passes for 293 yards to win his starting debut with the team that acquired him from the New England Patriots on Oct. 31.
Garoppolo completed all 14 of his pass attempts to his top two targets -- wide receivers Marquise Goodwin and Trent Taylor. Goodwin hauled in eight passes on eight targets for 99 yards, while Taylor caught six balls on six targets for 92 yards.
The quarterback threw his first career interception in 104 pass attempts, but the blemish looked worse on paper than it did in real time. The pass should have been a completion to wide receiver Louis Murphy Jr., but Bears cornerback Kyle Fuller ripped the ball out of the wideout's hands as he fell toward the ground.
"I thought it was a really good first start," 49ers head coach Kyle Shanahan said. "He handled the offense well. Definitely moved the chains and moved the ball well for us. It will be fun to get back and watch the tape and go through this stuff. Now, it's nice to be able to coach off this stuff and give him a chance to get much better."
Garoppolo grew up in the Chicago suburbs and spent time with his family in his hotel room on Saturday night. However, he said nearly all of his week was devoted to improving his knowledge of the 49ers' playbook.
Asked whether it was a relief to get his first 49ers start out of the way -- and to win it -- he grinned.
"I tried to say all week that it was just a normal game, but obviously I've never come back to Chicago like this," Garoppolo said. "It's exciting. It's one of the more fun games I've been a part of.
"This is the most confident I've been since I've gotten here, for sure. I think every week, it will just get easier and easier. We'll start putting more things in, adding to the repertoire. I think we're moving in the right direction."