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.
Pistorius testifies he didn't consciously pull trigger when he shot girlfriend
Pregnant Mila Kunis wins 'Best Villain' at MTV Movie Awards