"I know I'm capable of playing great tennis," the top-seeded Williams said. "Just haven't seen it yet."
Calling her performance "not professional," Williams was sloppy as can be for stretches in a 5-7, 6-3, 6-3 victory over 105th-ranked Anna-Lena Friedsam, a German who had never won a Grand Slam match until this week.
Williams committed 21 unforced errors in the first set alone, 52 in all.
"I was a little bit nervous [in the] first set," Friedsam said, "and I think Serena was a bit nervous too."
The American was particularly subpar with her serve, which she said she hasn't been able to work on properly in practice because of an elbow injury that led her to withdraw from a clay-court tournament in Rome this month.
"I'm not using it so much as a weapon," Williams said about her serve. "So hopefully it will get better."
She double-faulted eight times and allowed Friedsam to accumulate 15 break points, four of which were converted.
"I know my level is literally 100 times better than I played today," the 19-time major champion said, rolling her eyes, "so I think I take more solace in the fact I can play better, as opposed to the fact that that's the best I could play. Then I would be in trouble."
Next comes 27th-seeded
Even if she is 15-3 against Azarenka, including wins in the 2012 and 2013
The top-seeded Djokovic and Murray, seeded No. 3, both will take on talented young Australians for berths in the fourth round. Djokovic faces 19-year-old Thanasi Kokkinakis, while Murray meets 20-year-old
Coric eliminated 33-year-old
"All of them — Kyrgios, Kokkinakis and Coric — are showing some great skills and potential to be … top players," Djokovic said. "But it's a long way ahead."
Djokovic proclaimed the pain in his upper right leg "nothing serious, really" after taking a medical timeout late in the second set of his 6-1, 6-4, 6-4 win over Gilles Muller. For a few minutes, things did not look promising for Djokovic — prone on the court, getting massaged by a trainer.
But he eventually moved a step closer to completing a career Grand Slam. There was a gaffe at 4-1 in the third set, though, when Djokovic casually watched a ball by Muller sail long but touch the edge of his racket before hitting the court.
The point went to Muller, who broke there.
"Never, never, ever happened. And it should never happen again," Djokovic said. "I guess a little bit of lack of concentration. … It was funny to me, because I was 4-1 up, double-break. If it was 2-all, or 2-3 down, I wouldn't be smiling, for sure."
Murray stretched his post-wedding winning streak to 12 matches by defeating Joao Sousa, 6-2, 4-6, 6-4, 6-1.
Murray had won all 12 previous sets the pair had played against each other. So it appeared to be a big deal when Murray was cited for a time violation by the chair umpire shortly before frittering away the second set.
"I was struggling," Murray said. "There was pressure building."