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 not the respective fourth and sixth seeds – Romanian Sorana Cirstea and Czech Lucie Safarova.

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.”

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, who won 6-3 1-6 6-3.

The day’s biggest upset belonged to Canadian Sharon Fichman, who downed Cirstea 6-1 6-4.

There was also a one-sided victory for Czech qualifier Kristyna Pliskova, who 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.