"It hit the outside line," she told the chair umpire.
He disagreed — incorrectly — but Sharapova wasn't fazed for long. She overcame eight double-faults, the erroneous ruling and a second-set deficit to beat Zheng Jie 6-1, 7-5 in the third round Saturday at the French Open.
"I'm happy with the way I fought back and I found a way to win," said Sharapova, who completed a career Grand Slam by winning the Roland Garros title last year.
Seven-time champion Rafael Nadal had to come from behind yet again and reached the fourth round by beating Fabio Fognini 7-6 (5), 6-4, 6-4. After dropping the opening set in his first two matches, Nadal trailed 4-2 and was down a break at 6-5 before surging ahead for his 18th consecutive victory.
Nadal seeks to become first man to win eight titles at the same Grand Slam event. He next plays No. 13-seeded Kei Nishikori, who became the first Japanese man in 75 years to reach the fourth round at Roland Garros, beating Benoit Paire 6-3, 6-7 (3), 6-4, 6-1.
Sharapova will next play Sloane Stephens of the United States, who reached the fourth round for the second consecutive year by beating Marina Erakovic 6-4, 6-7 (5), 6-3.
Stephens was joined by two unseeded Americans reaching the round of 16 at Roland Garros for the first time. Julie Hampton defeated No. 7-seeded Petra Kvitova 6-1, 7-6 (7), and Bethanie Mattek-Sands beat qualifier Paula Ormaechea 4-6, 6-1, 6-3.
Like Sharapova, Australian Open champ Victoria Azarenka struggled with her serve, but she rallied past Frenchwoman Alize Cornet 4-6, 6-3, 6-1.
Seeded third, Azarenka hit 10 double-faults and was broken six times. She managed a smile later when asked about her serve.
"I think I left it home today," she said. "If I can win with serving like this, that's pretty remarkable."
She next plays unseeded Francesca Schiavone, the 2010 champion, who beat No. 13 Marion Bartoli of France 6-2, 6-1.
Sharapova found herself trailing 4-1 in the second set after the incorrect call. Facing a break point at 30-40, she hit a second serve that was ruled out.
The umpire climbed off his chair to check the mark and confirmed the call. Sharapova briefly argued in vain, contending the umpire looked at the wrong mark.
A TV replay showed her serve had indeed hit the line. The French Open is the only major tournament that doesn't use a video replay system, and Sharapova said that should change.
"It's not even about the fact of the call, whether it was in or out," she said. "The umpire did not recognize that the mark he pointed out was about a foot away from the actual mark."
Sharapova shook off the setback, sweeping the next three games to reach 4-all, and broke in the final game.