The Norwegian defender was deployed at right-back for the second match running following his impressive showing in the 3-2 win over Lille in midweek.
And the 22-year-old played a starring role again as Celtic got back to winning ways in the Scottish Premiership to close the gap on leaders Rangers to 13 points.
"I thought he was good," Strachan told Celtic TV. "He brought a lot to the game, and I thought he led. When you talk about [Scott] Brown and [Ryan] Christie not playing, I thought he led with his performance today.
"His enthusiasm getting forward, and his ability when he got forward. Good movement, good use of the ball, causing danger.
"And when the game broke down, he was sprinting back to get his position. Small things you don't see if you're not live at the game."
Ajer was awarded man of the match but in his post-match interview he insisted the award should have gone to Shane Duffy, who scored Celtic’s second goal with a powerful downward header.
Ajer said: "Today, I think it's the wrong man of the match. Today, Duffer deserved it.
"He's been through a lot and the way he's been in the dressing room and the way he performed today, I'm so delighted for him. So today I will give it to him."
Strachan disagreed, however, adding: "Misplaced humility. I do think [Ajer] was the far better player, but it's good that the players are looking after each other."