The golf outing put Key in rarified company. Obama is an avid golfer, but prefers to limit his playing partners to a close circle of friends and advisers.
Among those who have also scored invitations to play with Obama in the past are former President Bill Clinton and House Speaker John Boehner.
Media access to Obama's rounds is typically restricted, though reporters and photographers were permitted to briefly watch the two leaders.
The foursome pulled up to the green on the second hole in two golf carts, with the president and prime minister driving together. Obama's first putt was short of the hole and his second landed just wide.