So this might be his best chance to show the Patriots -- or another team that wants to trade for him -- that he's ready to be an NFL starter.
"Coach always has us guessing," the heir apparent said Thursday night after completing a Brady-like 22 of 28 passes for 235 yards and two touchdowns in a 31-24 loss to the Jacksonville Jaguars.
"You never know if you're going to play a little or a lot," said Garoppolo, who played two quarters and then went out for two more series in the second half while coach Bill Belichick sat the reigning Super Bowl MVP out. "When he put me back in, I was happy to get back out there with the guys."
Chad Henne hit Keelan Cole on a 97-yard touchdown pass, Corey Grant scored on a 79-yard run and the Jacksonville Jaguars feasted on a Patriots lineup without Brady and Rob Gronkowski -- or much defense at all -- to beat the defending NFL champions in their exhibition opener.
Garoppolo completed 13 straight passes at one point, finding Austin Carr on a 3-yard touchdown pass at the end of the first half and then K.J. Maye from 5 yards out to start the second and make it 17-17.
But the New England defense followed by giving up another one-play scoring drive -- this one Grant's run down the left sideline to make it 24-17.
"One of our basic plays. Coach called the play. The O line did their job. And then it was up to me to make that one guy miss," Grant said. "And then it was off to the races."
Third-string QB Brandon Allen hit Dede Westbrook from 42 yards out -- victimizing Patriots cornerback Cyrus Jones for another big play -- to make it a two-touchdown game. "We weren't expecting the touchdown, but everything worked out perfectly," Westbrook said.
Garoppolo was drafted in the second round in 2014 and has been stuck behind Brady, a five-time Super Bowl champion who has shown no signs of slowing down at 40 years old. The backup's big chance might have been last year, when Brady was suspended the first four games of the season, but Garoppolo only lasted five quarters before a shoulder injury knocked him out.
Unless Brady gets injured, these exhibition games are probably Garoppolo's only chance before he is eligible for free agency at the end of the season to show other teams he can play.
"He makes the throws and he led his team up and down the field," Jaguars defensive end Calais Campbell said. "I have a lot of respect for him and I am excited to see when he becomes a starter some day and see how he does."
Grant ran for 120 yards on eight carries for the Jaguars, who were playing their first game under new coach Doug Marrone after firing Gus Bradley following a 3-13 record. Executive vice president of football operations Tom Coughlin, the former New York Giants coach who twice beat the Patriots in the Super Bowl, watched from the press level.
Jaguars starter Blake Bortles completed 3 of 5 passes for 16 yards in two offensive series that resulted in one field goal. Henne came on with one play left in the first quarter and went 5 of 6 for 139 yards.
Patriots third-stringer Jacoby Brissett was 8 of 13 for 88 yards. He had a chance to tie or win the game with just over a minute left, but desperation passes sailed out of the back of the end zone on the final two plays of the game.
Jaguars: No. 4 overall draft pick Leonard Fournette ran nine times for 31 yards and a 1-yard touchdown.
Patriots: Undrafted free agent tight end Jacob Hollister, taking advantage of extra playing time with Gronkowski out, caught seven passes for 116 yards, including a 38-yarder. Carr, an undrafted free agent from Northwestern, caught five passes for 44 yards, going high to bring down Garoppolo's throw at the back of the end zone just before halftime.
Jaguars: Backup S Peyton Thompson left the game in the first half with a right biceps strain.
Patriots: Rookie DL Deatrich Wise left with a head injury in the first half.
NFL Commissioner Roger Goodell attended the game -- his first visit to Gillette Stadium since suspending Brady for four games in the scandal that came to be known as "Deflategate." Widely resented by New England fans, Goodell was spotted in Patriots owner Robert Kraft's luxury box at the start of the game.
After struggling in 2016 on special teams, the Jaguars hired Joe DeCamillis and brought in several specialists. Rashad Greene Sr. had a 41-yard punt return. Arrelious Benn had a nice tackle on a punt return.
AP NFL website: www.pro32.ap.org and www.twitter.com/AP-NFL
Can Seahawks afford to trade Russell Wilson?
Mina Kimes breaks down whether Russell Wilson and the Seahawks could part ways in the near future.
New Orleans mayor makes her pitch for Russ to join the Saints
New Orleans Mayor LaToya Cantrell lays out the reasons why she wants to see Russell Wilson with the Saints.
'Personable' Bill Belichick impresses at NFL Women's Careers in Football Forum
New England's boss helped lead a virtual session for aspiring coaches, stressing the importance of finding ways to keep learning and improving.
Ex-Notre Dame football star Louis Nix, 29, found dead after reported missing
Former Notre Dame star Louis Nix, a third-round draft pick of the Houston Texans in 2014, was found dead Saturday after he was reported missing earlier this week.
Brees gets workout in amid retirement rumors
Drew Brees puts in extra work during a training session.
Son of former Green Bay Packers DT Ron Kostelnik loses dad's Super Bowl II ring
The son of former Green Bay Packers defensive tackle Ron Kostelnik says he is heartbroken after losing his father's Super Bowl II ring and is offering a $5,000 reward for its return.