World number one Djokovic, playing in his first tournament since winning a ninth Australian Open in February, suffered his first defeat of 2021 on Thursday, DPA reported.
"Feels good to be back. I'm happy to be standing here regardless of if I won or lost. But obviously winning feels better," the 20-time Grand Slam champion said in the on-court interview after the match on Wednesday.
Ugo Humbert, who is on a seven-match winning streak after winning the Antwerp title last month, missed four match points but battled to a 7-6 (7/4), 6-7 (6/8), 7-6 (7/3) victory