Singh's addition Wednesday was a key boost for Woods, who last week said he was having a difficult time getting top golfers to commit for the July 5-8 tournament at Congressional Country Club. The tournament was added to the PGA TOUR calendar in March, after most players had set their schedules for the year.
Singh, ranked No. 6 in the world, has won three majors and has two victories this year on the tour.
Top 10 golfers Jim Furyk and Adam Scott have also said they will play. However, marquee names Phil Mickelson and Ernie Els are expected to skip the event.
Woods himself is uncertain if he will play because the tournament could coincide with the birth of his first child.
The AT&T National will be an invitation-only tournament with a 120-man field.
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