Loney tied the score at 1-1 in the third inning by drawing a bases-loaded walk off Jhoulys Chacin (9-11), and Kemp followed by blasting a pitch into right field stands to give the Dodgers the lead for good.
Loney drove in what turned out to be the decisive run with a fifth-inning RBI single, boosting Los Angeles to a three-game sweep of the Rockies at Coors Field.
Ramon Troncoso (2-3) picked up the victory with 1 1/3 scoreless innings in relief of starter Carlos Monasterios. Ronald Belisario earned his second save despite giving up a run and loading the bases in the ninth.
Troy Tulowitzki went 4-for-4 and scored four runs and Ryan Spilborghs collected three hits and drove in a pair of runs for Colorado, which dropped its ninth game in 10 contests.
The losing skid crushed their hopes of gaining a National League playoff berth. The Rockies were officially eliminated with Tuesday's loss to the Dodgers.