Johnson's RBI single capped a three-run first inning and his run-scoring hit in the sixth put the Rays ahead 4-2.
Roberts then followed with a two-run double to ice the contest for Tampa Bay, which took the rubber match of a three-game set at Coors Field.
James Loney went 3-for-4 with an RBI and three runs scored in the victory.
Alex Cobb (4-2) earned the decision, allowing three runs on eight hits over 6 2/3 innings. The right-hander walked one and struck out six.
Rockies starter Jhoulys Chacin (3-1) came off the disabled list (lower back strain) and was roughed up for six runs (five earned) on eight hits over seven full innings.
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