No.2 seed Ana Ivanovic has overcome first-match nerves and shoulder tightness to progress on a day of upsets at the ASB Classic tennis tournament.
Three qualifiers also made it through to the second round, but four seeds fell on Tuesday, including No.1 Roberta Vinci of Italy.
Vinci, the world No.14, was beaten by highly-rated Croatian teenager Ana Konjuh, who belied her youth with an impressive 3-6 6-4 6-2 victory.
Konjuh, the Australian and US Open girls' champion who is ranked 259 in the world, turned 16 last Friday.
Also out were the respective fourth, six and eighth seeds - Romanian Sorana Cirstea, Czech Lucie Safarova and Italy's Karin Knapp.
Ivanovic had to work for her 7-5 7-6 (7-2) win over American Alison Riske, saving five second-set points.
The Serbian, the world No.16, closed out the contest with a flourish, winning the last six points of the tie-break.
Ivanovic came away encouraged by her composure when behind.
"I was down a break in both sets so I was very pleased with the way I came back," she said.
"I kept composed at the important moments so I was very happy to finish in two sets."
Ivanovic twice got treatment on her right shoulder during the second set, but later said the problem wasn't serious.
She said she felt a bit of tightness after some mis-hit shots caused by a combination of the wind and early-season nerves.
Ivanovic went on to produce some big serving to get herself out of trouble at 3-5 and 0-40 down as Riske failed to convert four set points.
The former world No.1 and 2008 French Open champion saved another set point in the next game to level at 5-5.
"It was important to get that first win," she said.
"I was a little bit nervous going on court because I knew it was going to be a tough match."
While three qualifiers will join her in the last 16, the fourth - Estonian Anett Kontaveit - missed out only because she was beaten by another qualifier, Japan's Sachie Ishizu.
The two other qualifiers to progress were Canadian Sharon Fichman and Czech Kristyna Pliskova.
Fichman downed Cirstea 6-1 6-4, while Pliskova defeated Belgian Yanina Wickmayer - the 2010 champion and a two-time runner-up - 7-6 6-0.
Safarova went down to Japan's Ayumi Morita 7-6 (7-2) 6-3, while Knapp was beaten by German Julia Goerges 4-6 7-6 (7-3) 7-6 (7-2).
