Whether he did enough to win the backup job to Tom Brady remains to be seen.
Garoppolo threw for 284 yards and a touchdown in going the distance, but it wasn't good enough to keep the New York Giants from beating the Patriots 16-13 on Thursday night.
"It's one of those things I hope I look back on in a couple of years. I really learned a lot from it," Garoppolo said. "Now I've got to take it and try to take the next step. Now I know what a normal week is like, preparing to start. It will only help me going forward."
The biggest reason the Patriots (2-2) finished the preseason on a losing note was Belichick. He went for a first down in his territory late and it led to Josh Brown's game-winning 37-yard field goal with 38 seconds, capping the Giants' first undefeated preseason since 2006.
The gamble came on a fourth-and-1 from his 39 with less than three minutes to play and the score tied. Garoppolo threw his pass between two receivers and the Giants (5-0) ran off six plays to set up Brown's third field goal.
"It could have went better," Garoppolo said. "There are some things we messed up, fixable things."
The Patriots started just two regulars and trotted on Brady to hold on the first of Stephen Gostkowski's two field goals. Other than that he stayed on the bench for the defending AFC East champions while Garoppolo ran the plays.
"It will help his development," Belichick said. "He's obviously got a long way to go. He learned a lot from the week."
Belichick warned against reading anything more into it, defusing speculation Garoppolo had supplanted Ryan Mallett, Brady's backup last season, as the Patriots No. 2 quarterback.
"I haven't announced anything about any starters or anybody," Belichick said. "Last year hasn't anything to do with it. This year is this year."
New England opens the season a week from Sunday at Miami.
The Giants, who have missed the playoffs the past two seasons, play at Detroit in a Monday night game Sept. 8.
All the scoring came with reserves on the field and the Patriots were more impressive, with Garoppolo leading scoring drives of 82, 61 and 59 yards. He capped the first one with a 33-yard pass to Aaron Dobson early in the second quarter for a 7-3 lead. Gostkowski had field goals of 37 and 21, with the later giving New England a 13-10 lead late in the third quarter.
Brown, who beat out first-year kicker Brandon McManus earlier this week, tied the game in the fourth quarter with a 45-yarder. He had put New York ahead 3-0 following an interception by Zack Bowman in the second quarter. Peyton Hillis, who missed three weeks with an ankle injury, scored on a 1-yard run to put the Giants ahead 10-7 late in the half.
The Giants' new West Coast offense came into the fifth preseason game struggling, and it didn't show much in generating one first down against Patriots scrubs. Their final play summed up the preseason, despite the unbeaten record. On a third-and-2 from the Giants 28, Eli Manning hit tight end Kellen Davis for no gain.
A second-round pick out of Eastern Illinois, Garoppolo showed poise in his first start, completing 22 of 42 with a touchdown and an interception.
"I'm ready to move on to Week 1," Giants receiver Victor Cruz said. "I'm ready to get a good week of practice in come next week and get our focus onto Week 1 and starting the season off on the right foot, and I'm excited for that opportunity."