At that stage, it looked like Williams would race through the match and seemed to be an indication she was fit and firing for another assault on the world's top 10. The world No 47 could yet still make it but made too many unforced errors and had trouble with her serving rhythm to be totally convincing.
She was broken by the 27-year-old wildcard in the seventh game of the first set before breaking back immediately to regain control of the set and closed it out in 39 minutes.
Williams can still be a threat this week. Her name and record still intimidate some. She's won 44 career titles, including seven grand slams, and $35 million in career prizemoney and for a period in the last decade won 35 consecutive matches and six successive tournaments.
But she last won a grand slam titles in 2008 (Wimbledon) and has won only one title in the last three years, a second tier one in Luxembourg in 2012.
She was increasingly more timid and vulnerable in the second set as her serve deserted her and too many groundstrokes hit the net or looped long. She seemed to blame her racquet and in two games changed it twice.
Hlavackova had her chances as she grew in confidence, finally breaking Williams in the eighth game to serve for the set, but couldn't make it stick and was broken immediately. It was probably a good indication of why the 2013 US Open doubles and mixed doubles champion has never really made it in singles _ her highest ranking was 58 in September 2012.
Even then, Williams struggled. She served a double fault twice when on game point but ground her way to 5-5 before taking it into a tiebreaker.
Williams played more aggressively in the tiebreaker, perhaps sensing she needed to put more pressure on her opponent, and won it 7-1.
She looked relieved at the conclusion of the match, which sums up where she is at in her career. She is used to winning but it hasn't always come easily of late.
Williams will now face Austrian Yvonne Meusburger, who downed seventh seed Mona Barthel earlier in the day, in the second round on Wednesday.
She has a day to regroup, and will need that time.
ASB Classic - Day 2
Centre court 12pm
Monica Puig (PUR) vs Kirsten Flipkens (BEL)
Alison Riske (USA) vs Ana Ivanovic (SRB) [2]
Lauren Davis (USA) vs Marina Erakovic (NZL)
Not before 6.30pm
Roberta Vinci (ITA) [1] vs [WC] Ana Konjuh (CRO)
Andrea Hlavackova (CZE)/ Lucie Safarova (CZE) [1] vs Natalie Grandin (RSA)/ Sandra Klemenschits (AUT)
Court 4 12pm
[Q] Kristyna Pliskova (CZE) v Yanina Wickmayer (BEL)
Sorana Cirstea (ROU) [4] v [Q] Sharon Fichman (CAN)
Lucie Safarova (CZE) [6] v Ayumi Morita (JPN)
Not before 4pm
Karin Knapp (ITA) [8] vs Julia Goerges (GER)
Court 2 12pm
Lourdes Dominguez Lino (ESP)/Garbine Muguruza (ESP) vs Lucie Hradecka (CZE) Michaella Krajicek (NED) [3]
[Q] Anett Kontaveit (EST) vs [Q] Sachie Ishizu (JPN)
Tamira Paszek (AUT)/Coco Vandeweghe (USA) vs Karolina Pliskova (CZE)/ Kristyna Pliskova(CZE)
Paula Kania (POL) / Valeria Solovyeva (RUS) vs Sharon Fichman (CAN) / Maria Sanchez (USA)
Mona Barthel (GER) / Megan Moulton-Levy (USA) [4] vs Juliya Beygelzimer (UKR)
/ Maria Irigoyen (ARG)
Day one results
First Round
Jamie Hampton (5), United States, def. Tamira Paszek, Austria, 1-6, 6-0, 6-3.
Yvonne Meusburger, Austria, def. Mona Barthel (7), Germany, 6-4, 6-3.
Venus Williams, United States, def. Andrea Hlavackova, Czech Republic, 6-3, 7-6 (1).
Garbine Muguruza, Spain, def. Christina McHale, United States, 6-4, 6-3.
Johanna Larsson, Sweden, def. Lourdes Dominguez Lino, Spain, 7-5, 6-0.
Karolina Pliskova, Czech Republic, def. Paula Ormaechea, Argentina, 7-6 (2), 6-1.
Kurumi Nara, Japan, def. Alexandra Cadantu, Romania, 6-1, 4-0, retired.
Women's Doubles
Abagail Guthrie, New Zealand, and Sacha Jones, Australia, def. Cara Black, Zimbabwe, and Marina Erakovic (2), New Zealand, 3-6, 6-4, 13-11.
Kirsten Flipkens, Belgium, and Ana Ivanovic, Serbia, def. Irina Falconi, United States, and Eva Hrdinova, Czech Republic, 4-6, 6-3, 11-9.
Chin-Wei Chan, Taiwan, and Yi-Fan Xu, China, def. Kristina Barrois, Germany, and Renata Voracova, Czech Republic, 7-5, 5-7, 10-4.
