Augusta - World number one Dustin Johnson withdrew from the 81st Masters on Thursday, walking off the first tee due to a back injury.
The reigning US Open champion had been a heavy favorite in the year's first major golf championship after winning his three prior starts but suffered a lower back injury Wednesday in a fall down stairs at a rental house.
Johnson was seen walking back to the clubhouse shaking his head after undergoing a rigorous warm-up session before admitting defeat.
The 24-hour drama reached its emotional peak when Johnson arrived at the course and practiced his swings, hoping he could summon the strength to play through pain.
After a physical therapy session, Johnson tested his swing for several minutes under the watchful gaze of his caddie, brother Austin Johnson, and swing coach Butch Harmon, then returned for more therapy.
Johnson was to have joined two-time Masters champion Bubba Watson and 2016 PGA Championship winner Jimmy Walker in the day's final group.
Not since Rory McIlroy withdrew from the 2015 British Open has a world number one not played in a major championship.
The only other top-ranked player to miss the Masters was Tiger Woods, who did not play in 2014 after back surgery.