The tournament starts Sunday.
Vote here for who you think will come out victorious at Roland Garros. Barring Halep, the other four have won grand slam titles but are they still the names that are creating a buzz on the internet or draw spectators to the venue, we doubt?
Former world number one Williams, now ranked a lowly 453, is playing a Grand Slam for the first time since she won her 23rd major at the 2017 Australian Open after which she stepped off the tour to give birth to her daughter in September.
In contrast, 2010 champion Francesca Schiavone was the second oldest first-time grand slam victor at 29 years, 11 months and 14 days. Serena's fellow tennis star said the rule must change because it's not fair to women.
On Monday, organizers for the French Open tournament confirmed that they would not be seeding Williams this year because she took time off. And was 33 when she became only the third player - male or female - to win 20 major singles titles in 2015.
Twenty years on from her first appearance in the main draw at Roland Garros, Williams is in the unusual position of being unseeded for the coming fortnight - a somewhat controversial effect of her absence from the WTA Tour for more than a year either side of the birth of her first daughter in September.
Without a seeding, the 23-time Grand Slam champion risks facing highly ranked players in the early rounds.
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Drivers compensated by hydrating heavily before the race so they could complete a race that lasted more than three hours. She was in very good spirits early in the race, when she started on the inside of Row 3 and was running near the top 10.
Williams resumes her comeback after maternity leave following two consecutive losses in March.
Williams is 19-2 lifetime against Sharapova.
"I fell in love all over again with the sport and I enjoyed taking those few hours off from home to go and work out and play tennis, because I needed it, for various reasons, not just because I wanted to get back into shape".
Williams and Sharapova could meet in the fourth round of the French Open thanks to Thursday's draw, though a matchup between three-time champion Williams and two-time champion Sharapova is far from guaranteed.
Halep will open against Alison Riske, and Ostapenko will take on Kateryna Kozlova of Ukraine.
French Open 2018, year's second grand slam is all set to commence on May 27.
At the same time, by keeping a returning mother seeded, a player who has been fighting for 52 weeks for a high ranking would wind up losing out, as articulated by No. 15 seed CoCo Vandeweghe.