So why did Alexander pull himself out of the game midway through the first quarter?
"I probably was a little bit too [hyped]," Alexander said. "I was excited for the matchup and it was tough early on."
Whether defensive coordinator Mike Pettine asks Alexander to stick with one of Detroit's receivers -- either Marvin Jones Jr. or Kenny Golladay -- or decides not to match up in Monday night's game at Lambeau Field, don't expect Alexander's confidence to wane. Yes, Cooper went off for 11 catches, 226 yards and a touchdown. All but three of them for 25 yards came against Alexander (although at least one more -- a 23-yarder -- came against zone coverage).
One play after Cooper's second catch -- a 46-yard out-and-up in which Alexander jumped the out -- Alexander motioned to the sideline for a sub.
"I was out of breath; I couldn't breathe," Alexander said. "The first half of the game, it was hard for me to catch my breath in there. My legs felt so heavy, I don't know what it was. I warmed up pretty good, but I don't know. I had to come out though."
It didn't look like the Alexander who had dominated so many plays during the first month of the season.
"It started early in the game," he said. "Me and [Randall] Cobb were going at it first and then I got a little tired, then the next play Cooper wants to go at it with me, so it was just build-up."
He sat out the final two plays of the drive. They're the only two plays he has missed all season.
He needed oxygen on the sideline.
What he didn't need then and doesn't need now is a pep talk.
Alexander still broke up three passes against the Cowboys. He still had an interception on a ball Dak Prescott threw behind Cooper. He still leads the NFL in pass breakups with eight. And the Packers still won the game.
If you think he was moping around the team facility afterward, then you haven't been paying attention to Alexander since the Packers picked him at No. 18 overall in the 2018 draft. Alexander's swagger is, as Packers linebacker Blake Martinez put it, "Through the roof, no matter what."
"He was in the team meeting room, jumping around, shooting on the basketball hoop," Martinez continued. "It was a special thing to see because it makes me think, I want to be like that. No matter what happens, given any circumstance, I'm going to have complete confidence on the next play."
The Packers think they have a budding star in Alexander.
Just ask him.
This offseason, he told reporters he sees himself in the Pro Bowl and on the All-Pro team.
A week into the season, he billed the combination of he and fellow cornerback Kevin King as "the best tandem in the league."
When reminded of his comments from earlier this year, Alexander this week said: "I mean, every dog has their day. What's important is that we got the win and I don't have to think about that as much as if we would've lost. Got my hands on a pick, too, so I was favored in somebody's eyes, too. Every dog has their day. Some of the best corners have gotten beat way worse, so I'm not even ..."
Alexander couldn't even bring himself to say the words since they never enter his thought process.
"I love everything about Jaire," Packers coach Matt LaFleur said. "I think he competes on each and every play. He obviously had the big play with the pick that kind of got us going, but I love what he's all about, the energy he brings and I think he's a really good player."