Serena Williams and her preparations for the upcoming Australian Open were dealt a blow after the world number two suffered a defeat to Madison Brengle in the second round of the ASB Classic.
Top seed Williams was never really comfortable in the windy conditions in Auckland on Wednesday, stunned 6-4 6-7 (3-7) 6-4 by countrywoman and world number 72 Brengle.
Playing her first tournament since the US Open due to persistent shoulder issues, American star Williams was up and running against Pauline Parmentier on Tuesday.
And the 22-time grand-slam champion looked on track to advance to the quarter-finals after taking a 4-1 lead in the opening set.
Williams, however, struggled dramatically in the wind as Brengle won five successive games to take out the first set.
The 35-year-old failed to convince in the second set, squandering five set points as Brengle forced a tie-breaker but the former world number one dug deep to eventually send the match into a decider.
Brengle was not to be overawed, despite seeing two match points saved, as she earned a last-eight showdown with seventh seed Jelena Ostapenko.