Then, when the duo were in direct opposition as players a few years later in the second tier of German football, now Huddersfield Town head coach Wagner had the satisfaction of netting a hat-trick.
Klopp maintains to this day that he was softened up on the eve of that 1997 game by being invited over to the Wagner family home and being plied with copious amounts of food.
“I couldn’t make a proper challenge against him,” protested Klopp about a relegation battle that saw Wagner’s Gutersloh triumph 6-1.
Wagner, on being told of the Liverpool chief’s recollections 20 years on from a day when he was supposed to be marking the one-time United States international, laughed heartily before insisting his best mate, a right-back, had not been at fault for any of the goals.
“It was only my quality that created the goals,” said the Terriers’ chief with a huge smile. “Jurgen had done everything right. But, yes, he helped me because, before that day, I had not scored many goals for a long time.
“Of course, that day was a good one for me. Both teams were in relegation trouble so it was an important game for us.”
The mood between two men who are godfather to one of the other’s children may have been light-hearted during the build-up, but tomorrow will be a different matter as Premier League points – and, in Wagner’s case, a chance to leapfrog his old pal in the table – being up for grabs.
Liverpool, too, need a response to last weekend’s four-goal hammering at Wembley by Tottenham Hotspur.
Nevertheless, Wagner was yesterday willing to take a stroll down memory lane ahead of what will be the first meeting of two German managers in the English top flight. “Jurgen is more a family member than a friend,” said the Terriers’ head coach, who was best man at Klopp’s wedding. “We have a lot of fun, as you would expect from such good friends.
“We met at Mainz (in 1991) and here we are, at this point, where we will meet at Anfield in a competitive Premier League game.
“At Mainz, we were room-mates. Because he had a (young) child, he was pretty quiet and liked to sleep, like I did. Unfortunately, he was a smoker.
“That was not easy at the beginning, so I convinced him that he was only allowed to smoke in the toilet, and not in the room. He followed what I said.
“This was more or less the biggest discussion we ever had. Apart from that, it was perfect (to room together), because he more or less had the same rhythm that I had as a person.
“It meant we had hunger at the same time, we were thirsty at the same time and we went to bed and stood up at the same time.”
This bond, which began when Wagner was still 19, led to him performing best man duties at Klopp’s wedding in 2005.
It also means the duo enjoy poking fun at each other, Klopp claiming this week his friend as a player was, “Not very consistent, even if he does not want to hear it”.
Huddersfield boss Wagner responded in kind, suggesting the Liverpool chief was, “Technically average, endurance average”.
With this in mind, The Yorkshire Post asked Wagner if he found time during his best man speech to mention the hat-trick scored against Klopp.
“Usually, in a speech, you only talk about the nice memories of the man, not the worst memories,” he said, having previously admitted that alcohol had played a part in making recollections of Klopp’s big day hazy for a man who prefers a glass of cola to beer.
“But, okay, maybe over the years if he flies too high, then I will mention the hat-trick to him.”