Mack, who entered the 24-23 loss early in the first quarter, was involved in three game-altering plays that helped the Bears open a 17-0 lead at halftime.
"You prepare all offseason for the first game of the season, so I wanted to come back and make an impact, but you want to win these games," Mack said. "That is the only thing on my mind. I hate losing."
A former NFL Defensive Player of the Year, Mack was at times unblockable, tormenting Green Bay quarterbacks Aaron Rodgers and DeShone Kizer.
"I was pretty confident the Packers would have a hard time blocking him," Bears defensive lineman Akiem Hicks said.
At the 9:22 mark of the second quarter, Mack and Bears defensive end Roy Robertson-Harris broke through the Packers' offensive line and forced Rodgers to the ground. Robertson-Harris was credited with the sack, and the play resulted in Rodgers leaving the game with a knee injury. Rodgers later returned to start the second half.
Later in the first half, with Green Bay's offense picking up a little momentum behind backup quarterback Kizer, Mack registered a sack, forced fumble and fumble recovery -- all on the same play -- to thwart a Packers drive that had reached the Bears' 9-yard line.
With 50 seconds left before halftime, Mack intercepted a Kizer pass and returned it 27 yards for a touchdown.
Mack was officially credited with three total tackles and one additional quarterback hurry.
The Bears acquired Mack, 27, a 2020 second-round pick, and a 2020 conditional draft choice from the Oakland Raiders in exchange for two first-round picks, a 2020 third-round selection and a 2019 sixth-round pick.
Upon completing the deal, the Bears promptly signed Mack to a record six-year, $141 million contract.
"I love the game," Mack said. "When you love it, it's easy [to get ready to play without training camp or preseason]. That is really what it comes down to."
Mack records pick-six, fumble recovery in debut with Bears
Making his debut with the Bears, Khalil Mack has himself a game, with a forced fumble and recovery as well as a 27-yard pick-six against the Packers.