"Even, before I was number one and playing very successfully, winning trophies, he would say nice things about me when he was asked," Djokovic said as he prepared to defend his French Open title.
"And in the latest period when I was not as successful and was receiving a lot of criticism from many sides, Andre was one of the few people that was actually standing on my side and supporting me," said Djokovic.
"So I appreciate that very much, and I wanted to thank him in person, and over the phone."
A chat that was meant to be a quick marker between champions, lasted much longer than expected, said Djokovic. And from there it progressed to the point where Agassi was drafted in to fill the void after Djokovic removed his entire coaching staff at the start of May.
The pair will begin their work during the French Open, a tournament that is significant for both men.
In 1999 in Paris, Agassi came from two sets down in the final to beat the Ukrainian Andrei Medvedev and claim the crown. With it he became the fifth man to win at the four Grand Slam venues of Melbourne, Paris, London and New York.
Since then Roger Federer and Rafael Nadal have completed the fabled "career Grand Slam". Djokovic entered the pantheon in June 2016 following his four set triumph over Andy Murray in the French Open men's final.
Agassi, who won eight Grand Slams, retired from tennis after the 2006 US Open and has never coached professionally. But Djokovic says he believes he can learn from a man who has survived drama and spectacle on and off the court.
"That's one of the things I felt like I needed is new inspiration, someone that knows exactly what I'm going through, you know, on the court, off the court," added Djokovic. "He has been through all these transitions, he has been in my shoes before playing Grand Slams, being the best in the world, and facing all the challenges that are present in professional sport."
Agassi admitted this week that he was at first reluctant to take on the job as coach but was eventually persuaded by his wife, Steffi Graf.
"Novak called me about three weeks ago and I said I did not want to," said Agassi. "But Steffi said: Yyou should go, you will love it.' We had organised a family trip during Roland Garros anyway which was planned for a long time.
"So I hope to see one or two of Novak's matches and try to bring to him what I can because even a small remark can do a lot."