Paris - Jelena Ostapenko became only the second defending champion to lose in the first round of Roland Garros when she slumped to a shock 7-5, 6-3 defeat by Kateryna Kozlova of Ukraine on Sunday.
Russia's Anastasia Myskina was the only other defending champion to suffer the same fate in the first round in the Open era in 2005.
Ostapenko, who won her maiden tour title at the French Open 12 months ago with a breathtaking display of all-or-nothing big-hitting, drowned in a sea of errors on Court Philippe Chatrier.
The 20-year-old committed 48 unforced errors, 13 double faults and dropped serve seven times.
In all the four Slams, it's only the sixth time in the Open era that the defending champion has perished at the first hurdle.
"I really didn't expect anything from the match. Basically, I have hardly played for two and a half months but I wanted to show what I can do," said the 66th-ranked Kozlova who came into the match having played and lost just once on clay this year.
That came in Nuremberg last week, her first appearance on the tour since February because of a right knee injury.
On Sunday, Kozlova, who had defeated Ostapenko on grass in Rosmalen in 2016, was in the wars again, requiring a lengthy medical timeout at the end of the first set to treat blisters.
She then recovered from 0-2 down in the set before claiming victory when Ostapenko buried a backhand in the net on a second match point.
"One of the blisters was worse than the others, it was very bloody. But when you play a match, you try not to think about the pain."
Kozlova will face either former world number one Victoria Azarenka or Katerina Siniakova of the Czech Republic for a place in the last 32.
Second seed Alexander Zverev got his French Open title bid off to the perfect start with a 6-1, 6-1, 6-2 thrashing of Lithuanian Ricardas Berankis.
The 21-year-old, who arrived at Roland Garros on a hot streak of form after titles in Munich and Madrid before an Italian Open final loss to Rafael Nadal, stormed to victory in only an hour and 10 minutes.
Zverev lost in the first round last 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.
"I have won two tournaments, made the finals in Rome; again, losing to Rafa in a close match. I feel good, and today was a good start to the tournament, and I'm happy the way it's going so far," said the beanpole German.
Fourth seed Grigor Dimitrov also reached the second round, even if he wasn't exactly sure who he was facing.
Dimitrov had been drawn to face experienced Viktor Troicki in the tournament opener on Philippe Chatrier Court.
However, just before he was due to go on court, Troicki withdrew with a back injury, allowing Egyptian world number 182 Mohamed Safwat to make his Grand Slam debut.
In the process, he became the first Egyptian since Tamer El Sawy at the 1996 US Open to feature in a major.
"I was warming up and my coach said, 'hey look' and we saw up on the board that I was playing a different opponent," said 27-year-old Dimitrov, a former Wimbledon semi-finalist, after his 6-1, 6-4, 7-6 (7/1) win.
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.
"I only heard I was playing an hour before the match," said Safwat.
Seven-time major winner Venus Williams suffered back-to-back opening round exits at the Slams for the first time in her 21-year career.
The ninth-seeded, 37-year-old American slumped to a 6-4, 7-5 defeat to China's world 91 Wang Qiang, a player she knocked out in Paris last year.
Williams, playing Roland Garros for the 21st time, was in no mood for lengthy explanations after her loss.
"Nobody plans for this," she said.
Aussie firebrand Nick Kyrgios was forced to withdraw after failing to recover from an elbow injury, saying a potential five sets on clay was "too risky".
Kyrgios's withdrawal meant that eight places in the first round were opened up to lucky losers.
Women's fourth seed Elina Svitolina, a quarter-finalist in Paris in 2015 and 2017, overcame a first set 1-5 deficit to see off Australia's Ajla Tomljanovic 7-5, 6-3.
Svitolina next faces Slovakia's Viktoria Kuzmova who put out 2010 champion Francesca Schiavone, the 37-year-old Italian who made it through qualifying, 7-6 (7/2), 7-6 (7/2).
Results from day one of the French Open at Roland Garros on Sunday (x denotes seeding):
David Goffin (BEL x8) bt Robin Haase (NED) 4-6, 4-6, 6-4, 6-1, 6-0
Corentin Moutet (FRA) bt Ivo Karlovic (CRO) 7-6 (9/7), 6-2, 7-6 (7/5)
Martin Klizan (SVK) bt Laslo Djere (SRB) 7-6 (8/6), 4-6, 7-6 (8/6), 6-1
Gael Monfils (FRA x32) bt Elliot Benchetrit (FRA) 3-6, 6-1, 6-2, 6-1
Federico Del Bonis (ARG) bt Thomaz Belluci (BRA) 6-1, 6-3, 3-6, 6-1
Pablo Carreno Busta (ESP x10) bt Jozef Kovalik (SVK) 4-6, 6-1, 7-5, 7-6 (7/5)
Fernando Verdasco (ESP x30) bt Yoshihito Nishioka (JPN) 6-7 (4/7), 6-4, 6-3, 6-7 (3/7), 7-5
Guido Andreozzi (ARG) bt Taylor Fritz (USA) 6-7 (4/7), 6-3, 3-6, 6-2, 6-3
Jared Donaldson (USA) bt Nicolas Jarry (CHI) 6-3, 4-6, 3-6, 6-3, 6-4
Grigor Dimitrov (BUL x4) bt Mohamed Safwat (EGY) 6-1, 6-4, 7-6 (7/1)
Matteo Berrettini (ITA) bt Oscar Otte (GER) 3-6, 7-5, 6-2, 6-1
Kei Nishikori (JPN x19) bt Maxime Janvier (FRA) 7-6 (7/0), 6-4, 6-3
Lucas Pouille (FRA x15) bt Daniil Medvedev (RUS) 6-2, 6-3, 6-4
Damir Dzumhur (BIH x26) bt Denis Kudla (USA) 6-4, 6-2, 6-2
Radu Albot (MDA) bt Gregoire Barrere (FRA) 4-6, 0-6, 7-5, 6-1, 6-2
Alexander Zverev (GER x2) bt Ricardas Berankis (LTU) 6-1, 6-1, 6-2
Kateryna Kozlova (UKR) bt Jelena Ostapenko (LAT x5) 7-5, 6-3
Ekaterina Makarova (RUS) bt Zheng Saisai (CHN) 6-4, 6-1
Barbora Strycova (CZE x26) bt Kurumi Nara (JPN) 1-6, 6-3, 6-4
Yulia Putintseva (KAZ) bt Johanna Konta (GBR x22) 6-4, 6-3
Jennifer Brady (USA) bt Amandine Hesse (FRA) 6-1, 6-1
Petra Martic (CRO) bt Wang Yafan (CHN) 6-2, 6-3
Wang Qiang (CHN) bt Venus Williams (USA x9) 6-4, 7-5
Zarina Diyas (KAZ) bt Magda Linette (POL) 6-3, 6-1
Viktoria Kuzmova (SVK) bt Francesca Schiavone (ITA) 7-6 (7/2), 7-6 (7/2)
Elina Svitolina (UKR x4) bt Ajla Tomljanovic (AUS) 7-5, 6-3
Anett Kontaveit (EST x25) bt Madison Brengle (USA) 6-1, 4-6, 6-2
Magdalena Frech (POL) bt Ekaterina Alexandrova (RUS) 6-3, 3-6, 6-3
Sloane Stephens (USA x10) bt Arantxa Rus (NED) 6-2, 6-0
Alize Cornet (FRA x32) bt Sara Errani (ITA) 2-6, 6-2, 6-3
Suspended for darkness
Alexandra Dulgheru (ROM) level with Christine McHale (USA) 5-7, 7-6 (7/5)
Pauline Parmentier (FRA) leads Chloe Paquet (FRA) 3-6, 7-6 (7/4), 3-1