Seven double-faults, including four in one game; 37 unforced errors, and a first-serve percentage of just over 50 per cent that had her convinced "maybe I should have started serving lefty."
Some other numbers indicated why her 6-2, 6-3 loss to Russia's Ekaterina Makarova on what she admitted was a still-sore left ankle was more of a shock, particularly at this stage of the year's first major.
The American has played 43 singles matches at Melbourne Park since she won the first of her five Australian Open titles in 2003, and Monday's loss was just her third. She's 54-7 since playing here for the first time in 1998, and she hasn't gone out this early here since 2006.
"I'm not physically 100 per cent, so I can't be so angry at myself, even though I'm very unhappy," Williams said. "I know that I can play a hundred times better than I did this whole tournament."
Without Williams, who injured her left ankle in Brisbane two weeks ago, the only major winners still in contention were Maria Sharapova, defending champion Kim Clijsters and Wimbledon winner Petra Kvitova.
Sharapova earned the right to play Makarova in the quarter-final when she beat Germany's Sabine Lisicki 3-6, 6-2, 6-3 in a night match. The 2008 champion blew a 3-0 lead in the opening set, needed three set points to win the second and advanced on her second match point despite making 47 unforced errors and eight double-faults.
"A lot of ups and downs today — fortunately I finished on a high note," she said. "Even though I didn't play my best tennis I fought to the end and sometimes that's what gets you through."
Top-seeded Caroline Wozniacki, still in search of her first Grand Slam title, played Clijsters in a quarter-final on Tuesday. The Belgian veteran advanced to the quarter-finals with a comeback win over Li Na on Sunday in a rematch of the 2011 decider, while Kvitova had some trouble late before beating former top-ranked Ana Ivanovic 6-2, 7-6 (2) Monday.
Kvitova will next play Sara Errani of Italy, who beat 2008 semifinalist Zheng Jie 6-2, 6-1.
In the late night match, defending champion Novak Djokovic reached the Australian Open quarter-finals for the fifth straight year with a 6-1, 6-3, 4-6, 6-3 win over former No. 1-ranked Lleyton Hewitt.
Djokovic, who is aiming to become only the fifth man in the Open era to win three consecutive majors after collecting the Wimbledon and U.S. Open titles last year, was up two sets and a break before Hewitt won six straight games to force a fourth set.
But after losing a set for the first time in the tournament, Djokovic regained his composure to ensure all of the top five men reached the quarter-finals. He will next play No. 5 David Ferrer, who had a 6-4, 6-4, 6-1 victory over Richard Gasquet of France.
The loss for former U.S. Open and Wimbledon champion Hewitt ended his 16th campaign at the Australian Open and also meant there's no locals remaining in the men's or women's singles draws. Hewitt's best performance at Australian title remains his run to the final in 2005.
Earlier, two-time runner-up Andy Murray was leading 6-1, 6-1, 1-0 when Mikhail Kukushkin retired from their fourth-round match with a left hip injury, giving Murray an easy path into the quarters.
"It's obviously good for me, I get to conserve some energy," Murray said. "Tough for him, first time in the fourth-round of a Slam."
Murray will next play Kei Nishikori, who had a 2-6, 6-2, 6-1, 3-6, 6-3 win over sixth-seeded Jo-Wilfried Tsonga, the 2008 finalist.
The 22-year-old Nishikori became the first Japanese man in the last eight at the Australian Open in 80 years, and only the second man from his country to reach a Grand Slam quarter-final since the Open Era started in 1968. Shuzo Matsuoka reached the 1995 Wimbledon quarter-finals.
"Is feeling unbelievable. My first quarter-final and beating Tsonga, makes me really happy," Nishikori said. "I hope it's big in Japan. A lot of people messaged me a couple of days ago about the round of 16 and now the quarter-finals. It's really exciting."
Makarova, a 23-year-old Russian left-hander, was equally thrilled about her win over Williams. And considering she'd lost in the first round of the last six tournaments she'd played, in awe over who she beat.
"Yeah, I'm surprised because she's a great player and it's really tough to play against her. But, I don't know, I just feeling so good and so focus. So I played my game, and that's it. I won against Serena. That's amazing."
Makarova overcame plenty of Williams crowd support, many of whom weren't that familiar with the Russian. Oracene Price, Williams' mother, was in the players' box with her sunglasses on and a wide-brimmed hat.
In the fourth game of the second set with Makarova serving, Williams netted an easy forehand return. She made an angry sound, and there was a bit of laughter in the crowd. Price just turned away, shaking her head.
After Williams' fourth double-fault in the fifth game of the second set, which gave Makarova the game and a 3-2 lead — Williams shouted "Oh my God." She looked ready to smash her racket, but in the end bounced it on the court and caught it on the rebound.
The 13-time Grand Slam winner had only played two competitive matches since losing the U.S. Open final to Sam Stosur in September, and her light preparation was curtailed when she badly twisted her ankle as she won her second-round match at Brisbane earlier this month.
For that reason, Williams wasn't about to beat herself up over Monday's loss.
"Am I usually angry? I don't know. Crying? I don't cry. So I don't know what I usually project," she said. "I feel like I didn't play well today. I don't feel like I can't get better."
In first-round junior boys play, Vancouver's Filip Peliwo defeated Ken Onishi of Japan 3-6, 6-1, 6-4.
Peliwo and Serbian partner Pedja Krstin were also winners in first-round doubles, beating Australians Jacob Grills and Daniel Guccione 5-7, 7-6 (4), 10-7 tiebreak.
In girls' first-round action, Carol Zhao of Richmond Hill, Ont., downed Australian Brooke Rischbieth 6-2, 6-1.
Zhao and Montreal's Eugenie Bouchard, seeded eighth in the girls' doubles, defeated Megane Bianco of Switzerland and Kathinka von Deichmann of Liechtenstein 6-1, 4-6, 10-6 tiebreak in their first-round match.