Without a ball hit on Louis Armstrong Stadium, third seed Wawrinka progressed to the last 16 after Slovenia's Kavcic pulled out with a right foot injury.
The Swiss benefited from a retirement and a withdrawal early in his campaign at the Australian Open in January, when he won his first career major.
Wawrinka will take on either Spanish 16th seed Tommy Robredo or Australian teenager Nick Kyrgios for a spot in the quarter-finals at Flushing Meadows.