Serena Williams unveiled another new outfit at the US Open, but it was soon forgotten as she struggled to see off the challenge of Tatiana Golovin.
Williams eventually came through 7-5 6-4 in an entertaining match against the 16-year-old Frenchwoman.
But Golovin served notice of her considerable potential by taking a 4-1 lead in the first set and matching Williams' power throughout.
Twice former champion Williams now faces Patty Schnyder.
But she admitted she would have to improve after committing 42 unforced errors against Golovin.
"Nearly 50 unforced errors in two sets, that's almost giving away a set," she said. "I was going for far too much.
"When I was down 4-1, I still felt comfortable and relaxed but I couldn't get the ball in - I just wasn't looking at it.
"There were shots that I really should have made. I was playing two opponents, her and myself."
Jennifer Capriati saw off a second-set fightback by Vera Douchevina to advance to the fourth round with a 6-0 6-7 6-3 win.
The eighth seed blew away her Russian opponent in the first set but 17-year-old Douchevina forgot her nerves in an enthralling second set.
Capriati came back from 3-5 down to force a tiebreak but the Russian held firm to take it into a decider.
But Capriati eventually came through and will meet 12th seed Ai Sugiyama.
Capriati was given a test despite breezing through the first set
Capriati afterwards said Douchevina had a promising future.
"She made quite a few mistakes in the first set, probably nerves, but in the second set, she came up with some really good shots," she said.
"I've never even seen her play before, but she's good off the baseline and she's got an unbelievable backhand.
"But in the third set, I just took it up a notch and basically played more aggressive like I did in the first."
Amelie Mauresmo breezed into the fourth round after hammering Maria Vento-Kabchi of Venezuela.
The second seed fired eight aces and had 19 winners as she secured a 6-2 6-0 victory in 57 minutes.
Vento-Kabchi's humiliation was completed when she missed a smash and then double-faulted on the last two points of the match.
"It felt like things were coming together," said 25-year-old Mauresmo. "I felt much more comfortable."
She will play 16th seed Francesca Schiavone in the fourth round after the Italian edged out American wildcard Angela Haynes 6-3 7-6 (7-3).
French Open runner-up Elena Dementieva reached the last 16 without hitting a ball when Nathalie Dechy pulled out with a thigh injury.
Sixth seed Dementieva now plays fellow Russian Vera Zvonareva, who beat Colombia's Fabiola Zuluaga 6-4 7-5.
But there was disappointment for former world number five Daniela Hantuchova who suffered an agonising 6-4 4-6 7-6 (8-6) defeat to 15th seed Patty Schnyder.
Hantuchova served for the match at 5-3 in the decider and then squandered two match points in the tiebreak.