Johnson struck out nine in seven scoreless innings of a 3-2 Giants victory at AT&T Park, where it rained for much of the game.
Regardless of the result, the Rockies needed improved work from Jimenez (1-4), who gave up three runs and five hits in seven innings. He struck out five and walked two. After pitching seven scoreless innings against the D-backs in his first game of the season, Jimenez had gone 0-3 with a 12.00 ERA in three starts.
The loss, in the opener of a six-game National League West road trip, dropped the Rockies to 8-13. Still, they're seeing forward steps. No. 1 starter Aaron Cook has pitched well in the last two games after slumping to start the year. They could use a run of good work from Jimenez, their No. 2 pitcher.
"A lot of improvement was made tonight -- a very encouraging outing," Rockies manager Clint Hurdle said. "It's a professional job for a pitcher out there tonight. He just drew a tough match."
Johnson (2-2) struck out the first five hitters. His escape act came in the sixth, when he worked Todd Helton into a double play after Dexter Fowler and Matt Murton had singled with one out.
Johnson improved his career win total to 297, and he is 19-7 with a 2.23 ERA in 28 career starts against the Rockies.
"He's good," Rockies shortstop Troy Tulowitzki understated.
Hurdle marveled at a pitcher who is headed to being the Majors' next 300-game winner.
"He's 45 and he's been good," Hurdle said. "The next guy down the line is pretty far down the line."
Johnson said the Rockies have become a tougher opponent over the last several years.
"I have a great respect for the Rockies," Johnson said. "They have a very good lineup 1-through-8 with a lot of power. A lot of the hitters have some time under their belt, and they have a little bit more discipline."
Jimenez, 20 years Johnson's junior, showed some maturity Friday night.
Travis Ishikawa's double drove in a run with one out in the first, but Jimenez escaped without further damage. Jimenez walked the first two batters of the third and gave up a single and a walk to open the seventh, but each time limited the damage to one run, on sacrifice flies by Bengie Molina and Randy Winn, respectively.
"My last three games, I wasn't able to do that -- every time I had men on base, they scored," Jimenez said. "That gives me more confidence."
Rockies catcher Chris Iannetta broke the shutout with an eighth-inning leadoff homer off Bob Howry. Ian Stewart doubled and scored on Helton's single off Jeremy Affeldt. But Giants closer Brian Wilson fanned Ryan Spilborghs to end the threat with the bases loaded.
Instead of a rousing comeback, it was merely the Rockies' sixth loss in as many one-run games. They're 1-8 in two-run games.
"It's just a matter of capitalizing on those one or two opportunities throughout the course of the game, or making one or two other opportunities throughout the game so we'll come out on top," said Iannetta, who has homered on four of his nine hits this season.
Thomas Harding is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.