Ostapenko is the first French Open defending champion to lose in the first round since 2004 victor Anastasia Myskina dropped her opening match to María Sánchez Lorenzo in 2005.
Serena Williams, owner of three French Open titles and 23 major singles trophies overall, returns to Grand Slam action for the first time since winning the 2017 Australian Open - and first time since giving birth to a daughter last September.
Having taken the second set to level the match, Cornet then double-faulted on serve to gift Errani a break at the start of the third. Overall, she had won one of seven matches at any Grand Slam site. Safwat said. "I never saw the inside of that court before".
For Kozlova, it's the first time she's ever beaten a player ranked in the top 30. She was treated by a trainer during a medical timeout after the first set.
In her first second-round appearance at Roland Garros, Kozlova will play either Katerina Siniakova of the Czech Republic or Victoria Azarenka of Belarus.
Second seed Alexander Zverev is considered by many to be the main threat to Rafael Nadal's hopes of an 11th French Open triumph.
The former world No. 1, who missed much of last season after being embroiled in a custody battle over her son, has now won just two matches at Roland Garros in the last five years.
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The 28-year-old certainly has a habit of showing up and delivering when it matters most. "I hate when anybody gets hurt". It also comes from him just loving the game, loving to play and loving these moments, he just took full advantage of it.
Zverev lost in the first round previous year to Fernando Verdasco, but the German confidently avoided a repeat and enhanced his credentials as a serious threat to Nadal's hopes of an 11th title. "And, yeah, I'm just happy to be here again".
"It feels great", Kozlova said in press. The last Egyptian man to play at a major tournament was Tamer El Sawy at the 1996 U.S. Open. "I try to do everything what's in my power to play my best game on the Grand Slams", she said.
Safwat, 27, had lost in the final round of qualifying in what was his eighth futile attempt to make the main draw of the majors. "And also, from (other) players' side, like, every player you play wants to beat you".
The fifth-seeded Ostapenko, who upset Simona Halep in last year's final, lost 7-5, 6-3 against Kateryna Kozlova of Ukraine on Court Philippe Chatrier.
"Nobody plans for this", she said.
Australian Nick Kyrgios was forced to withdraw before his scheduled match with fellow countryman Bernard Tomic as he proved unable to recover from his elbow injury.
Rus was in the first round as a "lucky loser".