Serena Williams, playing the 1000th WTA match of her career, crashed out of the Italian Open on Wednesday with a second round defeat to Argentina's Nadia Podoroska, weeks before her bid to make history at Roland Garros.
Williams, 39, lost 7-6 (8/6), 7-5 on her return after nearly three months away to a player 15 years her junior who was a surprise semi-finalist at last year's Roland Garros.
"You know, it's tough to have a first match on clay," said Williams, who has won 73 WTA titles over the past two decades.
"It was definitely kind of good to go the distance and to try to be out there, but clearly I can do legions better.
"Maybe I do need a few more matches, so I'm going to try to figure that out with my coach and my team and see what we would like to do."
Williams, a four-time Rome winner and 23-time Grand Slam champion, had not played since her semi-final defeat to Japan's Naomi Osaka in the Australian Open this year.
And the eighth seed found it tough going, losing in just under two hours to the 44th-ranked Argentine.
"Overall, it was good for me to play such a clay court player on clay today, but it's a little frustrating," she conceded.
"Yeah, just filling out the game, finding the rhythm. Even sliding and confidence with that, with movement, and just not wanting to break my ankle when I moved.
"That's always like a little struggle in the first two matches, and then I'm raring to go."
The early exit is a blow three weeks before the French Open in Paris on May 30 where the American continues her bid to equal Australia's Margaret Court's record of 24 Grand Slam trophies.
Despite a battling performance Williams could not wear down the 24-year-old who broke twice in the first set.
Podoroska forced a tie-break with an ace and squandered three set points before sealing the set.
In the second, Williams was trailing 5-2 but held and broke the Argentine to love while she served for the match to level at 5-5.
- 'Special win' for Podoroska -
Podoroska held her nerve to earn three match points to secure just her third career win over a top-10 player, all in the last eight months.
"It's a special win, she's a great athlete, she's done so many things for our sport," said Podoroska who next meets Croatia's Petra Martic.
"It's history most of all."
For Williams it was her 149th defeat, with 851 wins over the course of a WTA career spanning 1000 matches.
But she will not get to celebrate with the Rome public, with spectators only allowed from Thursday's third round at the Foro Italico while limited to a 25 percent capacity.
World number one Ashleigh Barty advanced to the third round with a 6-4, 6-1 win over Kazakh Yaroslava Shvedova.
But second seed Osaka of Japan slumped to a 7-6 (7/2), 6-2 loss to American Jessica Pegula.
Days after her shock defeat in the Madrid Open final, Barty overcame an early break of serve to see off Shvedova, a three-time Grand Slam quarter-finalist making her way back after giving birth to twins.
Playing with her left thigh strapped, the Australian dropped her opening service game but rallied to level at 4-4 as she won 11 of the final 13 games.
Barty will next meet 28th-ranked Russian Veronika Kudermetova as she bids for a first Rome quarter-final on her third appearance.
Osaka, a four-time Grand Slam winner, had received a first-round bye, but was unable to find her way back into the match after losing the first-set tie-break to her 31st-ranked opponent.
Osaka was playing just her third tournament since winning the Australian Open in February and also exited in the second round in Madrid earlier this month.
Osaka, the reigning US Open champion, has seven career hard-court titles, but has never managed to lift a clay-court trophy.
Former Rome champion Karolina Pliskova, seeded ninth, also advanced along with fifth seed Elina Svitolina of Ukraine.