Pittsburgh (70-44) took two of three at home from Colorado (52-64) last weekend. Liriano (12-4, 2.02 ERA) won his third straight start Saturday by allowing two hits in seven scoreless innings in a 5-2 victory.
"I'm just going out and pitching and trying to be aggressive and get people out," said Liriano, who overcame five walks. "It's working out well for me and it is working out well for the team because we're winning."
De La Rosa (10-6, 3.31), meanwhile, gave up three runs over four-plus innings while striking out three and walking two.
"Jorge didn't have very good command," manager Walt Weiss said. "It was a struggle for him from the start."
De La Rosa's thumb flared up last month, but he said that wasn't a problem. The left-hander gave up eight runs in a 9-8, 10-inning loss to Atlanta on July 29.
"There are no excuses," De La Rosa told the Rockies' official website. "This is the second bad game in a row. I have to fix that, quick, because I can't keep pitching like I pitched."
His two poor outings were on the road. De La Rosa is 6-1 with a 2.65 ERA in 10 home starts, with the Rockies winning eight of them. He is 25-5 in his last 38 starts at Coors Field, and Colorado has lost just six of those games.
He has yielded two runs over his last 18 innings at home while Liriano has allowed one over his last 21 2-3 overall.
The Pirates figure to have Andrew McCutchen back in their lineup after the star was scratched Thursday in a 5-4, 10-inning victory over Miami because of discomfort in his right shoulder. McCutchen singled as a pinch-hitter in the seventh and is 11 for 17 over his last six games.
The Pirates completed a three-game sweep in which they trailed in every game, rallying from a four-run deficit in the fifth inning Thursday. Pittsburgh's bullpen worked 10 1-3 scoreless innings in the series.
"We're like the Miami Heat," McCutchen said. "We play better in the second half of games."
The Rockies, playing without the injured Carlos Gonzalez, are coming off a 1-9 trip that was capped by Thursday's 2-1 defeat to the Mets. They have lost five straight, totaling six runs while hitting .205 with 34 strikeouts.
"I know it hasn't been pretty on the road this trip," Weiss said. "The bottom line is you've got to make adjustments constantly in this game. Figure out how people are getting you out and make the necessary adjustments. It's a constant battle."
The Pirates have won two of three at Colorado in each of the three previous seasons.