Victory at the Bridgestone Invitational last night followed his success at the Open Championship a fortnight ago.
Starting the final day three shots off the lead, McIlroy won by two strokes from Sergio Garcia.
One man highly unlikely to make the tee at Valhalla on Thursday is Tiger Woods.
He withdrew from the Bridgestone Invitational less than halfway into his final round, complaining of back spasms
The 14-time Major winner underwent surgery for a back problem at the end of March and made his return just three months later at the Quicken Loans National.