De La Rosa earned his first road win of the season, striking out eight and holding the Reds to two hits in 6 2/3 innings. The Rockies earned their eighth victory in nine games since the All-Star break, 5-1, at Great American Ball Park in front of 33,981.
Add that to his previous start -- one run in six innings in a victory over the Pirates. Suddenly, De La Rosa (5-5), whose career has been notable only for its maddening inconsistency, has put together rare consecutive stellar starts.
"It's only two games that I've been pitching like this," De La Rosa said.
The Rockies have increased their chances to holding serve in the National League West -- they're six games behind the also-streaking Diamondbacks -- with such starting pitching.
Since the All-Star break, Rockies starters are 8-1 with a 3.62 ERA. And that includes the lone loss, when Kip Wells gave up eight runs, seven earned, in one-third of an inning.
The left-handed De La Rosa, 27, was on the brink of being dropped from the rotation at the break.
"The focus is improving, and obviously the ability to slow the game down when he's got to get back in the stretch," Rockies manager Clint Hurdle said.
It's not as if De La Rosa has mastered the art of calm. But he's learning.
De La Rosa held the Reds without a hit until two were out in the fourth and Ken Griffey Jr. hit the 607th home run of his career to tie the game at 1. After that, De La Rosa gave up just one hit, but he also issued four of his five walks and faced a couple of troublesome situations.
But for the second straight game, he offered arguments against his reputation for unraveling with runners on base.
De La Rosa walked Joey Votto to open the third, but forced David Ross into a double play. De La Rosa walked two in the fifth, but also struck out Adam Dunn, Votto and Andy Phillips.
Each time runners were on base, and as the crowd was lauding Griffey, De La Rosa made conspicuous efforts to calm himself by stepping off the mound, pulling off his hat, and breathing deeply.
"I've been working with 'Dac' [pitching coach Bob Apodaca] to try to control my emotions," De La Rosa said. "I think that's helped me a lot."
Hurdle has noted that De La Rosa has meshed with No. 2 catcher Yorvit Torrealba. It's an odd mix -- a pitcher who is being urged to control himself with a demonstrative catcher.
"It's definitely funny, because I'm the one that's jumping and getting all excited, but I need to find a way to make sure I slow him down because that's what he needs," Torrealba said.
With two on and two out in the seventh, De La Rosa had help from reliever Manuel Corpas, who worked a fly ball from Javier Valentin.
De La Rosa needed patience with a Rockies offense that for nearly five innings did everything except score.
The Rockies lashed 15 hits in 4 2/3 innings against Reds starter Homer Bailey (0-4), but the game was at 1 until they lashed four runs on six straight hits in the fifth.
The Rockies had two runners caught at the plate.
Reds center fielder Jay Bruce threw out Torrealba in the fourth. Griffey, from right field, erased Brad Hawpe at the plate in the fifth, when Troy Tulowitzki forgot to move into position to alert Hawpe to slide. Hurdle said, "That doesn't work -- 'Tulo' is aware of it."
Finally in the fifth, Tulowitzki and Torrealba knocked RBI singles, and De La Rosa popped a two-run single -- his second hit in 21 at-bats this season.
What the Rockies lacked in efficiency, they made up for in the patience department. They had 16 hits -- their seventh straight game with at least 11 -- but just one for extra bases. Garrett Atkins' third-inning double might have driven in a run had Matt Holliday not been doubled off at first earlier in the inning.
"Sometimes we do hit the long ball, but sometimes we work counts, grind out some at-bats and get base hits," Tulowitzki said.
Thomas Harding is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.