Mladenovic rallied in the third set, despite battling through multiple stoppages due to lower back issues and only scoring 11 points on the second set during the warm afternoon. The two-hour, 24-minute clash at center court ended after a 6-4 upset of Kerber, sending Mladenovic onto the second round.
“I just said to give it my all,” Mladenovic – a two-time Grand Slam doubles champion – said afterward.
The French player also defeated the German great when Kerber was ranked in the top-five in 2017. Kerber expressed a level of disappointment following her early exit.
“It was not my best match, but she played a good tactic against me,” Kerber said at the press conference. “I played good in the second set and it was an up-and-down match. The first rounds are always not so easy, especially since I played not so well in the last few weeks.”
In round two, Mladenovic will face fellow countrywoman Fiona Ferro.
Elsewhere at the US Open, all-time greats Venus and Serena Williams made quick work of their respective opponents, Saisai Zheng and Maria Sharapova.
The elder Williams defeated Zheng 6-1, 6-0, and will face fifth-ranked Elina Svitolina on Wednesday. Serena Williams disposed of Sharapova 6-1, 6-1 in just under one hour, accumulating her 19th consecutive victory over the former world number one.
Top-seeded and 2018 US Open Champion Novak Djokovic steamrolled over 76th ranked Roberto Carballes Baena, 6-4, 6-1, 6-4, in less than two hours.
Djokovic, who is in pursuit of a fourth US Open title and 17th Grand Slam Singles Championship, improved to 14-0 in US Open first round match-ups following the dominant showcase.
“At this stage of my career and my life, it’s mostly about Grand Slams really,” Djokovic offered candidly at the post-match presser. “That’s the thing that matters the most in the history of our sport and certainly motivates me the most. I do value every tournament I play, but these are the events where I want to perform my best.”