Liriano (12-4) overcame five walks with the help of three Pirates double plays while yielding just two hits and striking out six en route to his second win of the week.
In the two starts, the left-hander allowed just one run over 14 innings while fanning 14.
The 29-year-old is off to his best start since going 12-3 with Minnesota in 2006, a season that left him with an arm injury that led to his undergoing Tommy John surgery.
Mark Melancon posted his sixth save for the National League Central-leading Pirates, who broke a two-game skid and moved 1 1/2 games in front of second-place St. Louis.
Tabata's solo blast in the fourth inning put the Bucs ahead 2-0 and Gaby Sanchez supplied two run-scoring singles for Pittsburgh.
Rockies starter Jorge De La Rosa (10-6) lasted just four innings, yielding three runs on six hits.
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