Grand Slam champions Jelena Ostapenko and Sofia Kenin joined their fellow major titlist Naomi Osaka as first-round winners at Roland Garros on Sunday.

It was not a perfect day for Grand Slam singles champions, though, as Barbora Krejcikova was upset by Viktorija Golubic.

Ostapenko advances: Former Roland Garros champion Ostapenko of Latvia became the first Top 10 seed to reach the second round of this year's edition, defeating Jaqueline Cristian of Romania 6-4, 7-5 on Court Suzanne Lenglen on Sunday.

No.9 seed Ostapenko, who famously stormed to her first career singles title as an unseeded player at 2017 Roland Garros, needed 1 hour and 34 minutes to get past a tricky first-round opponent in World No.69 Cristian.

Coming into Paris, Cristian had already won 10 matches on clay this year (including main-draw and qualifying victories). She reached the quarterfinals at Charleston, beating Madison Keys en route, then posted third-round showings at WTA 1000 events in Madrid and Rome.

Meanwhile, Ostapenko's Roland Garros results have been spotty since her title. In her last six appearances, Ostapenko's best Paris performance has only been a third-round showing in 2020. Cristian had also beaten Ostapenko in their sole previous meeting, at 2021 St. Petersburg.

Indeed, Cristian started the stronger of the pair, breaking Ostapenko in the first game and holding that advantage through 4-3. However, the easy power of Ostapenko began to reveal itself and the Latvian claimed a break to love to level affairs at 4-4.

A backhand return winner gave Ostapenko another break to wrap up the one-set lead, during a stretch where she won five straight games. Cristian stopped that streak by breaking for a 2-1 lead in the second set, but Ostapenko eventually regained level footing.

As light rain began to fall and the retractable roof on Court Lenglen started to close during play, Ostapenko failed to serve out the match at 5-3, despite clawing back from 0-40 to deuce.

However, at 6-5, the 2017 champion broke Cristian at love, with the Romanian firing her third double fault of the day to end the clash. Overall, Ostapenko used her sterling groundstrokes to blast to victory, with 28 winners to Cristian's 10.

Ostapenko will play Denmark's Clara Tauson in the second round, after World No.72 Tauson defeated Tatjana Maria 6-2, 6-3 on Sunday. Former top-ranked junior Tauson beat Ostapenko in the 2021 Luxembourg final, but Ostapenko avenged that loss earlier this year in Linz.

Kenin prevails: Kenin of the United States, who won the 2020 Australian Open title and hit a career-high ranking of World No.4, battled past Laura Siegemund of Germany 4-6, 6-2, 6-2 on Court Simmone Mathieu on Sunday.

Dimitar Dilkoff/AFP via Getty Images

Kenin, who also reached the 2020 Roland Garros final before losing to a then-unseeded Iga Swiatek, survived a spirited challenge from Siegemund, a former Top 30 player who won her biggest career singles title on clay at 2017 Stuttgart.

After losing the first set, World No.56 Kenin stormed to a 5-2 lead in the second set, but a lengthy rain delay derailed her progress after she missed out on two set points in that game. Upon resumption of play, Kenin faced a break point but was able to rebound and close out the set.

In the third set, Kenin won key points with her crosscourt backhand and pinpoint returns, building a 4-0 lead. Kenin stared down a total of five break points in her last two service games, but she held firm to clinch a Roland Garros second-round spot for the first time since 2021.

In the second round, Kenin will face French No.1 Caroline Garcia, the No.21 seed, who also won on Sunday. Kenin has won both of their previous meetings in straight sets, but this will be the first time they face off on clay.

Golubic ousts former champ Krejcikova: Late in the day, 76th-ranked Golubic toppled 2021 Roland Garros champion Krejcikova 7-6(3), 6-4 on Court Suzanne Lenglen.

It took Switzerland's Golubic 1 hour and 41 minutes to upset No.24-seeded Czech Krejcikova just before 10 p.m. local time, leveling their head-to-head at three wins apiece.

Krejcikova battled from 4-0 down to 6-5 up in the first set, but the former World No.2 could not serve out the set, and the pair moved into a tiebreak. Golubic again grabbed an early 4-0 lead in the breaker and held on for the one-set lead.

In the second set, Krejcikova again came back from a break down, firing a backhand winner down the line to reach 4-4. But Golubic reclaimed that break in the very next game, then used a backhand to force a Krejcikova error and convert her first match point.

Golubic reached the second round in her Roland Garros main-draw debut in 2016, but this is her first main-draw win in Paris since then. The Swiss has peaked at World No.35 and reached the Wimbledon quarterfinals in 2021.

As for Krejcikova, since winning the 2021 title, she has lost in the first round at Roland Garros three straight times. The Czech reached the Australian Open quarterfinals earlier this year, but she is currently in the midst of a five-match losing streak on tour.