He announced the birth of his daughter Sunday, a day after he withdrew from the Canadian Open while in front after wife Kandi went into labor.
He tweeted: "What a whirlwind of a day."
He said Zoe Olivia Mahan was born at 3:26 a.m. in Texas.
Mahan was leading the tournament in Oakville, Ontario, after two rounds Saturday. He flew home to Dallas when his wife went into labor a month before her due date.
He said in another tweet his wife and daughter are "doing great." He thanked his sponsors for appreciating "what's important in life" and saluted his fans for "being Awesome!"
Mahan would have been on the course at Glen Abbey for the third round when his wife began having labor pains, but his tee time was delayed 80 minutes by a thunderstorm.
Brandt Snedeker won the tournament Sunday.
"Zoe will be getting a very nice baby gift from me," Snedeker said. "I can't thank Kandi enough for going into labor early. I don't know if I'd be sitting here if she hadn't. But that is a way more important thing than a golf tournament. I missed a golf tournament when my first was born, and it was the best decision I ever made. I'm sure Hunter would say the same thing."