On another, she pushed a backhand into the net while her feet gave way, yet again leaving her awkwardly splayed on the grass at Court 2, the same place where her sister Venus lost a day earlier.
By the end, the younger Williams was screaming after nearly every point, good or bad — and, well, there were plenty of both. Her harder-than-the-score-looked 6-2, 6-4 victory over the 62nd-ranked Barbora Zahlavova Strycova of the Czech Republic in the first round at the All England Club wasn't exactly perfect or pretty.
"Definitely a little relief," the sixth-seeded Williams said. "I was letting out a lot of cries. I was happy to get through that."
Yes, Williams got the job done, something she couldn't say the last time she was at a major championship. Last month at the French Open, the 30-year-old American tossed away a big lead — nine times, she was two points from victory — and lost to a woman ranked 111th, the only first-round exit of Williams' career in 48 Grand Slam tournaments.
"I learned that you got to ... keep going," Williams said about that stunning defeat. "I was really disappointed. Obviously, I was extremely disappointed. But as Kelly Clarkson says, 'What doesn't kill you makes you stronger.'"
In part because of a series of health scares that sidelined her for about 10 months, Williams has gone two years since the most recent of her 13 major titles, including four at Wimbledon. And even though she bowed out quickly in Paris, Williams is a popular pick to do well this fortnight.
"For me, when I'm playing a match," Williams said, "I either win it or lose it."
She'll want to play better than she did against Zahlavova Strycova, who is 0-21 against top-10 opponents, 13-27 in Grand Slam matches, and never has made it past the third round at any major.
Some other top players were sluggish at the start against unheralded foes Tuesday, when action was cut short in the evening because of rain.
Two-time Wimbledon champion Rafael Nadal, for instance, trailed 4-0 against 80th-ranked Thomas Bellucci of Brazil before turning it around and winning 7-6 (0), 6-2, 6-3.
"Fantastic for me," Nadal said, "but I have to improve a lot for the next round."
Defending women's champion Petra Kvitova fell behind 3-0 and 4-1 but eventually used a seven-game run to take control and beat 96th-ranked Akgul Amanmuradova 6-4, 6-4. The match was halted by a 30-minute rain delay in the second set; when they returned, Kvitova needed all of three minutes to wrap things up.
"In the beginning," Kvitova acknowledged, "I think I was nervous."
Twelve singles matches were suspended in progress and four were postponed altogether. Among those that began but didn't finish, 2003 U.S. Open champion and three-time Wimbledon runner-up Andy Roddick led British wild-card entry Jamie Baker by a set and a break; French Open finalist Sara Errani was a point from beating U.S. qualifier CoCo Vandeweghe; and 21st-seeded Milos Raonic of Thornhill, Ont., was a game from eliminating Santiago Giraldo of Colombia, leading by two sets and 5-4 in the third.
It was a mixed day for the Canadians.
Aleksandra Wozniak of Blainville, Que., beat Russian Vera Dushevina 6-2, 7-5 but Stephanie Dubois of Laval, Que., dropped a 4-6, 6-4, 6-3 decision to China's Zheng Jie. American Sam Querrey defeated Vasek Pospisil of Vancouver, 7-5, 6-7 (5), 6-3, 6-4.
In men's doubles, Toronto's Daniel Nestor and partner Max Mirnyi of Belarus survived a scare in the first set to eventually beat Americans Michael Russell and Donald Young 4-6, 6-0, 6-2, 6-1.
In singles play, winners included 10th-seeded Mardy Fish of the United States, playing his first match since having a medical procedure on his heart a month ago. The 30-year-old Fish hit 24 aces and defeated Ruben Ramirez-Hidalgo of Spain 7-6 (3), 7-5, 7-6 (1), then didn't attend a postmatch news conference; a tour spokesman said Fish wasn't feeling well, but didn't elaborate.
All three Australian men in action Tuesday exited, meaning none reached the second round at the All England Club for the first time since 1938. No. 20 Bernard Tomic, a quarterfinalist at 18 years old in 2011, was knocked out by David Goffin, the Belgian wild-card recipient who took a set off Roger Federer in the fourth round of the French Open; 2002 Wimbledon champion Lleyton Hewitt lost to No. 5 Jo-Wilfried Tsonga; and Matthew Ebden was beaten by Benoit Paire of France.
"The boys didn't have the best day," said Hewitt, who used to be ranked No. 1 but has dealt with a series of injuries, is now 202nd, and needed a wild card to get into the field.
He hadn't bowed out in the first round at Wimbledon since 2003. Williams never has. Never lost before the third round, actually, and now is 13-0 in openers at the grass-court Grand Slam tournament.
Last year, Williams questioned why tournament organizers assigned her and her sister to play on Court 2 rather than the larger and more prestigious Centre Court or Court 1. They have, after all, won a total of nine singles championships at Wimbledon and faced each other in four of those finals.
Given that Venus lost in straight sets on Court 2 on Monday, and Serena went through a workout to win there on Tuesday, the issue came up.
"I can't even talk about it. I'm over it," Williams said, raising her left palm. "I just can't talk about that right now. I'm not in the mood."
Follow Howard Fendrich on Twitter at http://twitter.com/HowardFendrichSuggest a correction