The 29-year-old left Wednesday's hosts for Anfield eight-and-a-half years ago, but time has not deteriorated the relationship between player and fans.
A glowing smile lit up Agger's face as he skippered the travelling contingent at the familiar Brondby Stadion, where Brendan Rodgers' side were overturned 2-1.
"The fans said it all - the way they reacted and the way they were singing," the centre-back, who clocked up 45 minutes, explained to LFCTour.com later.
"Everything was really emotional for me. I haven't been here for so many years and that was the reaction I got. It was overwhelming.
"It was good to be back. I really miss this place, I have some really good memories from here and they all came back on the pitch."
The meeting with Brondby was Liverpool's first fixture of a busy pre-season schedule as they prepare for the resumption of domestic football and the prospect of the Champions League.
Agger continued: "That's the place you want to be and we are there now. That will be exciting.
"Football is about winning; it's not just being there, it's about winning. It has to be like that for Liverpool Football Club.
"You have to build; we have to do better this year, even though it's going to be difficult. There have been a lot of good new signings. Hopefully we learned a lot from last year and we can take it from there."