Jason Day will push on in pursuit of the US PGA Tour's season-long $US10 million jackpot after his family escaped unscathed from a car accident in Boston.
The world No.1 opened with a one-under-par 70 at the second FedEx Cup playoff event before learning a car carrying his wife and two young children was rear-ended by a bus.
Day made a hasty departure from the Deutsche Bank Championship but officials say he has decided not to withdraw after earlier fears that he may have to pull out.
"After the completion of my round today, I was informed my wife Ellie our children Dash and Lucy and friend Katie were involved in a traffic incident near our RV," Day said in a statement.
"Their car was hit by a bus and Ellie was taken to the hospital for precautionary measures.
"Thankfully everyone is now resting comfortably and Ellie has been released.
"They will all be monitored in the coming days.
"We want to thank the emergency services and hospital personnel for their assistance."
Entering the tournament, Day was sitting in second spot in the season-long points race for the $US10 million ($A13.24 million) bonus jackpot.
His off-course issues on Friday mirrored his rollercoaster round.
After starting on the 10th hole, Day had three bogeys, two birdies and an eagle on the par-five second to finish the day five shots behind American first-round leaders James Hahn and Ryan Moore, who both fired six-under 65s.
Englishman Paul Casey, Argentine Fabian Gomez, American Brian Stuard and Jhonattan Vegas of Venezuela all had 66s to share third place just one back.
Adam Scott, fourth in the points race, returned a four-under 67 to be the best of the Australians two strokes off the pace and in a tie for seventh.
Marc Leishman (68) is equal 19th, and Aaron Baddeley (69) and John Senden (69) joint 38th, with all three needing strong finishes to make the field for next week's third playoff event, the BMW Championship at Crooked Stick.
FedEx Cup leader Patrick Reed shot a 68 to be three behind Hahn and Moore after the first round.
The accident involving Day's family comes nine months after Ellie was concussed and taken to a Cleveland hospital when basketball superstar LeBron James crashed into her while she and her golfer husband were courtside at an NBA game last December.