Edmund is the heir apparent to Andy Murray’s reign at the top of British men’s tennis but he was outclassed by the crafty Mannarino, who won 6-2 7-5 6-4.
The 21-year-old’s serve was a particular cause for concern as he produced 10 double faults and was broken seven times in the match.
Edmund had shown good form coming into this tournament, pushing Murray to three sets at Queen’s two weeks ago after beating then-world No 18 Gilles Simon for the biggest victory, in ranking terms, of his career.
But the youngster from Beverley was well below his best on Court Two against a tricky opponent, known for his excellent touch and variety, but one he would have considered beatable when the draw came out on Friday.
“I thought I just played quite inconsistently today,” Edmund admitted afterwards. “With the way I was constructing points, I didn’t put enough pressure on him.
“My serve was quite inconsistent. I served well in patches and in patches it went off. In the second and third set I broke him back, but you want to be breaking to go ahead in the match. It was a shame because I always felt I was playing catch-up.”
Edmund, usually so consistent from the baseline, lacked rhythm early on as three double faults helped left-handed Mannarino clinch two breaks and a 4-1 lead.
The world No 68 was given temporary hope when he clawed one break back but Mannarino was the more comfortable and served out to take the opening set.
Edmund was struggling with his timing as his whipping forehand twice caught the ball on his frame and another break in the first game of the second put Mannarino firmly in charge.
Loosening up, Edmund started to match his opponent from the back but Mannarino’s superior variety meant he continued to dictate the rallies.
Edmund even broke back to level at 5-5 but a simple forehand missed down the line let Mannarino back in and he served out for a two-set lead.
For the third set in a row, Edmund lost an early service game but he broke back when a limp Mannarino lob got the treatment it deserved.
Parity, however, was short-lived as more wayward serving gave Mannarino the chance to close out the match, which he did with ease, as a final Edmund return dropped into the net.