While the Bears defense had its own problems against the Green Bay Packers in the second half of a 24-23 defeat, it was Trubisky whose play left the most visible room for improvement after the opener.
"He played the way I knew he could play," Nagy said Monday after the Bears let a 20-0 lead in the third quarter turn into another disappointing loss to their rivals. "He made some plays. Now we left some out there, too, but that's gonna happen.
"Shoot, there's some plays that their guy, No. 12 left out there too other than the second half. For the most part, Mitch is going to learn, he's going to keep growing. He understands that. First thing he said to me on the bus was, 'how can I get better' That's the best part about him and where we're at right now.
No. 12, Aaron Rodgers, did almost nothing wrong despite a knee injury, but Trubisky still had the chance to lock up the game and couldn't get it into the end zone in the fourth quarter. Then he took a fourth-down sack at his own 38 with the Bears trying to get into field goal range with a two-minute drill.
Early on, Trubisky hit on his first seven passes before finishing poorly.
Whether it was inexperience showing, or the effects of the Packers adjustments and pass rush, Trubisky seemed quick to abandon passes to scramble with the game on the line.
"There were some good ones, and there were a few where I thought his clock was ticking a little too fast," Nagy said. "You get the pocket collapse a little bit, and I thought that instead of just sliding and then hitching forward, it was a run. He kind of dashed out of there.
"He knows that. That's going to be the neat part as you see this thing go and you see him grow, is he's going to see those things. He's not the guy that will do that again. He'll learn from that."
Quarterbacks coach Dave Ragone said Trubisky displayed other strengths not evident because of the loss.
"There was other things where you appreciate a lot about his toughness," Ragone said. "There's no blink in him in the pocket. If there's a guy coming at him, he's not going to blink."
Passing-wise, a pass allowing Robinson to go up in a jump ball situation for a 33-yard gain was a step in the right direction. Robinson hadn't caught a pass in training camp, and Trubisky had never shown the ability to complete this type of throw last season.
"I thought the big throw to a Rob early in the game up the sideline shows great improvement in terms of trusting his guy and giving his guy a chance to make a play," Ragone said. "And obviously, Allen did that for him."
Trubisky struggled to a 77.2 passer rating and was 23-for-35 with 171 yards and no turnovers. He had a 77.5 passer rating for his 12 starts last season.
"There's going to be things that don't show up in a quarterback rating that we want to see from an improvement for him to be able to build on his foundation," Ragone said. "And some of those things showed up."
Trubisky cited some mid-game problems with three-and-outs as an example of the opponent outguessing the Bears. Two three-and-outs in the third quarter and at the start of the fourth were followed by Packer touchdown drives.
"We expected a lot of man (coverage) on third-and-short and they came out and played a bunch of zone," Trubisky said. "Credit to them for just mixing it up.
"A lot of our calls were built for man. We had some risky calls that we just went with and we blew them, and they just made plays that we didn't."
The young quarterback wasn't the only one having problems. Nagy admitted to trouble with his play calling.
"I go back personally, we ran two screens back to back and I didn't like those calls," Nagy said. "I told the guys those were on me."
Running back Jordan Howard had 83 yards and seemed to be gaining momentum as the game hit the middle of the fourth quarter. Yet the Bears went away from him on a few key third-and-short plays and had drive-killing incompletions.
"I liked what Jordan did," Nagy said. "Jordan is one of those guys that once he gets the ball he gets rolling. And you could see that.
"He ended up with 15 carries. In a perfect world you'd like to see him get a few more carries."
In a perfect world, the Bears would have preserved a 20-point lead, as well.
--LB Khalil Mack played more than most anticipated he could after only one week of practice with the Bears following a training camp-long hold out in Oakland. He had 42 plays, or 70 percent of the defensive snaps. Mack became the first player since sacks became an official statistic in 1982 to have a sack, interception, touchdown, forced fumble and fumble recovery all in one half. He had three tackles for the game. "You prepare all offseason for the first game of the season, so I wanted to come back and make an impact," Mack said. "But you want to win these games. That is the only thing on my mind. I hate losing." Mack had an ice pack on his hand after the game but said he was OK.
--LB Leonard Floyd played with his right hand in a ball cast and had two tackles, including one for loss. Floyd normally is one of the quieter defenders, but succinctly summed up the difference between the Bears losing 24-23 to the Packers and losing the way they did twice last season under John Fox. "It feels way different, because we have a bunch of guys that want to win," Floyd said. "Tonight, we displayed that we wanted to win, but we need to learn how to finish."
--LB Danny Trevathan suffered a minor back injury in Sunday's game but returned to play.
--S Eddie Jackson was one of the defenders standing up to take heat after Aaron Rodgers authored a comeback win. "The whole team got lazy," Jackson said. "We got too complacent, especially on the defensive side of the ball. We didn't finish. We came out the first half swinging. The energy was there. The second half I felt like the energy was low. Everybody got complacent, and we lost focus that we still had a game to finish."
--LB Roquan Smith made a sack of DeShone Kizer on his first NFL play. The Bears limited Smith because of a tender hamstring and his lack of practice time in the defense. He finished with three tackles and a hurry in his first career action.
--DE Akiem Hicks made his first career sack against the Packers. He forced a fumble on the sack, but Green Bay recovered. Hicks also had three tackles.
"We challenged him, and I thought he stepped up," Bears coach Matt Nagy said. "You could see he made a couple big plays in there. He's a force. Even trying to double-team him, it's hard. He splits the double team."