Leading the tie 5-1 and with a set point, Mladenovic's drop shot seemed to bounce twice on the side of her opponent Laura Siegemund.
But instead of awarding the point and the set to the 27-year-old Frenchwoman, umpire Eva Asderaki told her she had lost the point for touching the net. Mladenovic pleaded with the official about the double bounce but to no avail.
Siegemund eventually held her serve to trail 2-5 on Court Philippe Chatrier.
Mladenovic then squandered the opportunity to claim the set 6-2 despite having another set point on her own serve.
Wasteful
She racked up five more set points while Siegemund was serving at 3-5 down. But she still could not convert.
Siegemund eventually levelled as Mladenovic's game started to unravel in a fashion similar to the meltdown she suffered nearly a month ago at the US Open where from 6-1, 5-1 she squandered four match points on her way to a three set defeat.
The 32-year-old German took full advantage of the diffidence to claim the opener 7-5.
"Kristina started solidly," Siegemund told the post-match interviewer Cedric Pioline. "I was making a lot of unforced errors but I tried to find my groove and cut down my mistakes and while I was doing that she made a few more errors."
Competition
A contest appeared plausible at the start of the second set when Mladenovic claimed Siegemund's serve to end the six game roll
But it was a fleeting fillip. Siegemund hit back immediately for 1-1 and she made the decisive break when Mladenovic was serving to level at 4-4.
Unlike her opponent, she did not fluff her lines at the crunch. "I played point by point," Siegemund said. "I tried to fix the errors and I wasn't thinking about the big picture. Even if I was down I was trying to see what the problem was and to fix it because it was only the first set and a long way to go.
Siegemund added: "I think in that situation at set point, that was a close call.
"That's what the umpire is there for. I think she has better chances than me to see what has happened exactly."
