The former world No.1 told reporters he felt unable to continue competing at the tournament and would leave to be with his mother before she undergoes surgery for lung cancer this week.
Defending champion Day stopped after a double bogey to fall three down against Pat Perez after six holes in Austin this morning, Australian time.
“At the start of the year, she (mother) was diagnosed with 12 months to live,” Day said at a press conference.
“This is so hard.
“The diagnosis is much better being over here and she is going for surgery this Friday.
“It’s really heard to even comprehend being on the golf course right now, because of what she has gone through.
“I’m glad I brought her over here because of it,” he said.
The 29-year-old Day said his family came before golf.
“It’s been really hard to play golf lately, this year. It’s been very emotional as you can tell.
“I’ve already gone through it once with my dad and I know how it feels. And it’s hard enough to see another one go through it as well.
“Emotionally, its been weighing on me for a while and I know my mum says not to let it get to me but it really has.”
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