Miami - World No 1 Serena Williams was forced to regroup but launched her bid for a ninth Miami Open crown on Thursday by defeating US compatriot Christina McHale 6-3, 5-7, 6-2.
Three-time defending champion Williams had the match on her racquet before having to withstand a fightback from her 23-year-old rival and taking two hours and seven minutes to reach the third round.
"She just started playing better, the kind of tennis she's never played before," said Williams. "I made a few mistakes and then I had to pull myself back together.
"I feel like I was just playing, but it's all right. I'm back now and I'm going."
Top seed Williams, who watched tournaments at the combined WTA and ATP hardcourt event as a child, will next face Zarina Diyas of Kazakhstan, who ousted Australian Daria Gavrilova 7-5, 6-3.
Williams fired 13 aces and 36 winners with 43 unforced errors while McHale responded with seven aces and 26 winners against 31 unforced errors.
Asked if she took McHale too lightly, Williams replied, "I don't underestimate anyone."
Williams, whose back-to-back finals losses at the Australian Open and Indian Wells were her first since 2004, served for the match in the 10th game of the second set but netted a backhand to surrender a break.
McHale held and won the first three points of the 12th game off Williams' serve. The 34-year-old pulled back two but swatted a forehand wide to force a third set.
"She definitely started fighting back," Williams said. "And she's clearly capable of playing great tennis."
McHale denied Williams on three break points to hold the first game of the final set but Williams broke in the third and smashed a backhand service return winner to break again in the seventh game.
Williams had to fight off two break points in the final game, saving one with her 12th ace and the other with a service winner, and she blasted her 13th ace on match point to finally advance.
After answering a few questions, Williams told reporters, "I just really don't want to be here. I feel like I've been doing press every day. That's enough," and ended her session.
Two-time Wimbledon winner Petra Kvitova reached the third round with a 6-1, 6-4 victory over 83rd-ranked American Irina Falconi.
"I served pretty well," the Czech eighth seed said. "She played better in the second set and that's what made it tougher. It's always a little bit tricky when it's someone you have never played before."
Kvitova next faces Russian 30th seed Ekaterina Makarova, who ousted Ukraine's Lesia Tsurenko 3-6, 6-4, 6-3.
British wildcard Heather Watson ousted US 20th seed Sloane Stephens 6-3, 6-0. She faces Belgium's Yanina Wickmayer in the third round.
Uzbek Denis Istomin rallied to beat Croatia's Borna Coric 4-6, 7-5, 7-5 to book a Saturday matchup with British second seed Andy Murray, who won their only two matches back in 2013.
Spanish fifth seed Rafael Nadal will open Saturday against Bosnian Damir Dzumhur, who rallied past Argentina's Leonardo Mayer 4-6, 6-3, 6-4.
Japanese sixth seed Kei Nishikori plays his second-round match against French qualifier Pierre-Hugues Herbert, who downed Czech Lukas Rosol 7-5, 6-4.
Japanese qualifier Tatsuma Ito beat Nicolas Mahut 7-6 (7/3), 6-2 to book a second-round match with another Frenchman, 16th seed Gael Monfils.
Roger Federer, a 17-time Grand Slam singles champion, will return Friday from an eight-week layoff for left knee surgery against Argentina's Juan Martin Del Potro, himself in only his third event back from a lengthy layoff after left wrist surgery.
The Swiss star has a 15-5 career edge on Del Potro but the South American won their biggest matchup in the 2009 US Open final.
World number one and defending champion Novak Djokovic, seeking his third Miami crown in a row and sixth overall, begins his title quest Friday against Britain's 87th-ranked Kyle Edmund.
Djokovic won last week at Indian Wells after taking his 11th Grand Slam title in January at the Australian Open.
Scores on Thursday from the third day of the ATP and WTA Miami Open (x denotes seeded player):
John Millman (AUS) bt Pablo Carreno Busta (ESP) 6-3, 6-2
Andreas Seppi (ITA) bt Donald Young (USA) 6-3, 6-1
Aljaz Bedene (GBR) bt Roberto Carballes Baena (ESP) 4-6, 6-2, 6-3
Andrey Kuznetsov (RUS) bt Rogerio Dutra Silva (BRA) 6-2, 6-3
Adrian Mannarino (FRA) bt Illya Marchenko (UKR) 2-6, 6-2, 6-3
Tim Smyczek (USA) bt Tommy Paul (USA) 6-4, 5-7, 7-5
Denis Istomin (UZB) bt Borna Coric (CRO) 4-6, 7-5, 7-5
Mikhail Kukushkin (KAZ) bt Brian Baker (USA) 6-4, 6-2
Tatsuma Ito (JPN) bt Nicolas Mahut (FRA) 7-6 (7/3), 6-2
Santiago Giraldo (COL) bt Paul-Henri Mathieu (FRA) 6-2, 2-6, 6-3
Denis Kudla (USA) bt Chung Hyeon (KOR) 6-3, 3-6, 6-1
Pierre-Hugues Herbert (FRA) bt Lukas Rosol (CZE) 7-5, 6-4
Damir Dzumhur (BIH) bt Leonardo Mayer (ARG) 4-6, 6-3, 6-4
Sergiy Stakhovsky (UKR) bt Nicolas Jarry (CHI) 7-6 (9/7), 7-5
Frederico Delbonis (ARG) bt Elias Ymer (SWE) 6-1, 4-6, 6-3
Marcos Baghdatis (CYP) bt Benjamin Becker (GER) 6-3, 6-4
Petra Kvitova (CZE x8) bt Irina Falconi (USA) 6-1, 6-4
Ekaterina Makarova (RUS x30) bt Lesia Tsurenko (UKR) 3-6, 6-4, 6-3
Timea Bacsinszky (SUI x19) bt Margarita Gasparyan (RUS) 6-3, 6-1
Ana Ivanovic (SRB x16) bt Tellana Pereira (BRA) 6-3, 6-0
Madison Brengle (USA) bt Anna Karolina Schmiedlova (SVK x28) 7-5, 6-4
Elina Svitolina (UKR x12) bt Zhang Shuai (CHN) 6-3, 6-0
Agnieszka Radwanska (POL x3) bt Alize Cornet (FRA) 6-0, 6-1
Yanina Wickmayer (BEL) bt Lucie Safarova (CZE x11) 6-2, 6-3
Heather Watson (GBR) bt Sloane Stephens (USA x20) 6-3, 6-0
Caroline Wozniacki (DEN x23) bt Vania King (USA) 7-5, 6-2
Caroline Garcia (FRA) bt Andrea Petkovic (GER x21) 7-6 (7/5), 3-6, 7-6 (7/2)
Julia Goerges (GER) bt Samantha Stosur (AUS x26) 3-6, 6-1, 6-4
Zarina Diyas (KAZ) bt Daria Gavrilova (AUS x31) 7-5, 6-3
Serena Williams (USA x1) bt Christina McHale (USA) 6-3, 5-7, 6-2
Svetlana Kuznetsova (RUS x15) bt Carina Witthoeft (GER) 6-3, 4-6, 6-4
Simona Halep (ROM x5) bt Daria Kasatkina (RUS) 6-3, 7-5