Italian Sara Errani and Germany's Mona Barthel, the respective second and eighth seeds, have been among the casualties on the first day of the ASB Classic.
Two seeds have fallen on the opening day of the ASB Classic in Auckland, with Italian Sara Errani and German Mona Barthel both making quick exits.
After No.2 seed Errani lost to Slovakia's Daniela Hantuchova 6-3 6-2, eighth seed Barthel was upset by 17-year-old Croatian Ana Konjuh 6-2 6-1.
Errani, the world No.14, fought back from dropping the opening set to an opponent ranked 48 places below her to get an early break in the second.
But Hantuchova then took over the contest between two former world No.5s, rattling off the last six games to win in one hour and 15 minutes.
She was pleasantly surprised at how well things went for her in her opening match of the season.
"Sara is obviously a great fighter and a great player and for a first round to have a draw like that was not easy," she said.
"I knew I had to be extremely focused for every single point, because she is very good at turning matches around."
Hantuchova was particularly pleased with her intensity, her movement and the technical aspects of her game she had been working on.
She will face either another Italian, Francesca Schiavone, or Polish qualifier Urszula Radwanska in the second round.
Earlier on Monday, sixth seed Sloane Stephens made it three wins out of three for Americans on the opening day.
Stephens, the world No.36, took just over an hour to get past Spain's Silvia Soler-Espinosa 6-3 6-1.
Her next opponent will be fellow American Lauren Davis, who overcame compatriot Shelby Rogers in a lengthy three-setter.
While Stephens' win was relatively straight-forward, Davis had to mount a big comeback before prevailing 1-6 6-4 6-3.
There are seven Americans, headed by seven-time grand slam winner Venus Williams, in the 32-strong main draw, making them the largest national contingent.
Also among them is wild card Taylor Townsend, who downed former champion Yanina Wickmayer in three sets.
Townsend, 18, produced some heavy shot-making, none more so than in the second game of the final set as she broke her Belgian opponent to love.
The world No.104 went on to close out a 7-5 3-6 6-0 win over Wickmayer, a player ranked 30 places above her.
"I was really happy I was able to fight through," the former world No.1 junior said.
"I was fighting through a lot of different things - nerves, myself, the old things, some of the new stuff I had been working on."
Townsend now awaits the winner of the match between top-seeded Dane Caroline Wozniacki and Israeli qualifier Julia Glushko.