Elise Mertens from Belgium and Emma Raducanu of Great Britain have withdrawn with injuries ahead of their opening games in the Auckland tournament.
Raducanu has suffered a back injury and while she had hoped for a speedy recovery, it has not improved sufficiently for her to compete.
The US Open champion was set to play her opening round match against American Robin Montgomery on Tuesday evening.
"I've tried my best to be ready. I love Auckland and the fans here. But unfortunately, I've picked up a back niggle and I won't be ready in time," she said.
Mertens, the world No 21 ranked female, also withdrew Tuesday morning ahead of her first-round match.
"I am sorry not to play my singles due to an injury. I wish the tournament all the best and hope to be back next year."
Their places have been taken by Mai Hontama from Japan and Jodie Burrage from Great Britain, respectively.
Kiwi hopeful and world number 40 Lulu Sun lost her first round match yesterday to Canadian Rebecca Marino.
Americans dominant
It's looking likely the tournament will be a heavily American affair. Top seed Madison Keys safely advanced with a 6-4 6-4 win over Lucia Bronzetti on Tuesday.
Although her Italian opponent put up a decent fight, Keys' experience shone through in windy conditions at Stanley Street.
"It was a little tough, but to be expected. Really happy to say I had a pretty clean match despite the conditions," Keys said after the match.
"It always feels really good to get the first win of the season. We're all a little bit more nervous and a bit more out of sorts so to get that win really helps the confidence and momentum."
That momentum is likely to continue in the second round when she faces unseeded Romanian Jacqueline Cristian.
Keys, from Florida, joined compatriot Sofia Kenin in the winner's circle today, meaning eight American players will take the court in the second round.
Kenin had to work hard in the first set of her match against Wang Xiyu, before running away with the second to win 7(7)-6 6-1.
Like Keys, she said that adjusting to the wind quicker than her opponent was deciding factor.
"I kept my serve, which is not easy. These conditions, you just have to hit the ball through the middle and try to be aggressive and not passive," said the world No 23, who now doesn't have to deal with Raducanu on her side of the draw.
While Kenin would have gone in confident, as she has won the last two matches between the two, it was a different feeling for tournament director Nicolas Lamperin regarding the loss of the two big names through injury.
"She obviously hasn't been able to train properly ahead of the new season," he said regarding Raducanu's ongoing lower back injury. Mertens' injury was unknown.
"When athletes want a chance to play, they will give themselves up till the last minute before making a decision. You have strong objectives… it is a setback for sure. You want to start strong and get as many matches before the Australian Open."
