Cabrera Bello bounced back from an opening bogey with birdies on four of the next five holes, and then added four birdies on the first six holes of the back nine.
Bradley, who started the day in second place behind Spanish overnight leader Rafa Cabrera Bello, turned in six birdies to go with a pair of bogeys.
"I woke up Sunday and I couldn't really walk", Day, ranked No. 11 in the world, told Golf Channel's Will Gray.
British Open champion Francesco Molinari made one of two aces on the day - the other belonged to D.A. Points - and was among those at 69.
The 34-year-old from Las Palmas, who teed off on the 10th, nearly capped a superb performance with an ace at the par-three second, drilling his tee-shot to within a foot of the pin.
Giants Trade Olivier Vernon to Cleveland in Exchange for OG Kevin Zeitler
The 28-year-old had cap hits of $19.5 million in 2019 and 2020 from the five-year, $85 million contract he signed in 2016. There is depth at that position in this year's class, and Cleveland could land one with the No. 17 overall pick.
India asks Pakistan for concrete crackdown on terror groups：The Asahi Shimbun
Pakistan also detained the MiG-21 pilot Wing Commander Abhinandan Varthaman, who was handed over to India on Friday. One day later Pakistan responded with fighter jets crossing into Indian-administered Kashmir .
Indian high commissioner to Pakistan returns to Islamabad
The Indian high commissioner will also engage on urgent issues not only with Pakistan but with diplomats of other countries in Islamabad .
"Playing with Sam is always a pleasure, not because he's the grandson of Arnie but because of how nice of a guy he is, " Cabrera Bello said.
Jason Day's Players Championship campaign is in serious doubt after withdrawing mid-round on day one at the Arnold Palmer Invitational at Bay Hill in Florida.
"And I think sometimes I'm too much of a fan of the game because I know exactly who has won the Grand Slam, and I know exactly the people I would be putting myself alongside". The top three players not already exempt from the top 10 at Bay Hill will get into Royal Portrush.
"My back was sore when I was practicing from Tuesday to Saturday, and I was going to practice on Sunday, but I woke up and couldn't really walk or sit in the vehicle".
"I've been making sure I get my driver turning over (right-to-left) as that's something I've struggled with the last couple of years at the Masters".
Day was one of just three Australians to start the week, Aaron Baddeley the best of the remaining two after 18 holes with a 2-under 70 to be T15.