Both sides saw open chances go begging, and a second-half penalty was the decider in favor of the hosts.
KC defender Ike Opara missed a golden opportunity to tap in an open goal in the 17th minute. The ball beat 'Quakes keeper Jon Busch to the back post, but unmarked with half the goal gaping in front of him, Opara's awkward touch pushed the ball into the post, where it rebounded back off him and wide, out of play.
Sporting was awarded a penalty in the 56th minute, with Steven Lenhart whistled for handling the ball in a penalty-area scrum, and Dom Dwyer converted from the spot.
Chris Wondolowski wasted the best chance San Jose had to come back, firing wide with only the keeper to beat from 10 yards out in the 72nd minute after taking a layoff from Lenhart.
Sporting's MLS record for 2014 is now 1-1-1, while San Jose is 0-1-1.