Jason Day says his mother's lung cancer surgery in Ohio has gone well.
In a text message delivered by his agent Friday, Day said his mother is resting comfortably and that doctors are optimistic about her recovery.
Dening Day was diagnosed at the start of the year in Australia, and the initial prognosis was that she had 12 months to live.
Jason Day brought his mother to Ohio for more tests, and the surgery was performed at the James Cancer Center at the Ohio State University.
"Emotionally, it's been wearing on me for a while. My mom says not to let it get to me, but it really has," Day said Wednesday. "This has been very, very tough for me. I'm going to do my best and try and be there the best I can for her because she is the reason that I'm playing golf today."
Day withdrew from the World Golf Championships-Dell Technologies Match Play after six holes Wednesday because he wanted to be with her for the surgery.
"It's really hard to even comprehend being on the golf course right now," Day said. "It's been really hard to play golf lately. It's been very, very emotional, as you can tell. I've already gone through it once with my dad. And I know how it feels."
His father, Alvin, died of stomach cancer when Day was 12.
Day entered the year as the world's No. 1-ranked player. He has since dropped to No. 3, with one top-10 finish in five starts. His next start is expected to be at the Masters in two weeks.
Information from ESPN's Jason Sobel and The Associated Press contributed to this report.