Graffanino's pinch-hit bloop single scored Geoff Jenkins from third with one out in the 10th inning, sending the Brewers past the Rockies 2-1.
"I've been working on that in batting practice," Graffanino deadpanned.
Derrick Turnbow (2-3) pitched a scoreless 10th for the victory.
Jenkins broke an 0-for-14 slump by hitting the first pitch in the 10th off LaTroy Hawkins (0-4) to the left-center field wall for a double. Tony Gwynn grounded out to second, moving Jenkins to third, before Graffanino hit a soft fly that landed a few feet past the infield in center field.
"They had their infield in, so I knew I had enough of it that it hopefully would reach the outfield grass," Graffanino said.
The utility infielder was pinch-hitting for Rickie Weeks, who is in a 3-for-42 slump.
"I'm very uncomfortable doing it, but I just felt it was the right thing to do," Milwaukee manager Ned Yost said of the move. "Rickie's been struggling a little bit.
"It's not something I enjoy doing because Rickie's a kid who gives you everything he has," Yost added. "But at this point in the season I have to put the team first. That's what I did."
All-Star Ben Sheets pitched 3 1/3 innings, giving up one run and two hits while striking out three before leaving with a sprained middle finger. The right-hander grimaced immediately after throwing a pitch to Todd Helton in the fourth and was replaced by Yovani Gallardo.
X-rays were negative, but the team said Sheets would undergo an MRI exam on Monday if it continues to bother him. Sheets said he didn't think the injury was serious.
"I'm kind of optimistic. I think I'll be all right," Sheets said.
It was the second time this year he has been removed due to a hand injury. He left in the seventh inning May 22 at Los Angeles because of a blister.
Colorado starter Rodrigo Lopez didn't allow a hit until Corey Hart snapped a 1-for-17 slump with his 12th home run of the year with two outs in the sixth, tying the game at 1-1. The ball barely cleared the left-field fence and the glove of leaping left-fielder Ryan Spilborghs.
"It is a game of inches and in that case, I missed it by 2 inches," Spilborghs said. "If I was 2 inches taller or I could jump higher, I would have had it."
Hart's homer was the only hit allowed by Lopez in seven innings. He struck out five and walked two, exiting after seven innings and 97 pitches.
"It was a tough one," Lopez said. "I can't remember the last time I had a one-hitter over seven innings. It was too bad we came out with a loss."
Spilborghs hit his sixth home run of the year in the third, giving the Rockies a 1-0 lead.
Gallardo pitched 4 2/3 innings of scoreless relief, giving up only one hit that later was erased by a double play.
The Brewers managed only four hits while Colorado had three.
"It was outstanding pitching on both sides," Yost said. "Two good hitting ballclubs shut down by opposing pitchers."
- It was the first time in 19 games that the Brewers won while scoring less than three runs.
- The Brewers lowered their team flag to half mast outside Miller Park Saturday to commemorate the eighth anniversary of the accident that killed three workers building the stadium in 1999.
- The crowd of 42,559 was the Brewers 14th sellout in 45 home games. Last year, the team had 14 sellouts the entire season.
- Lopez had been 1-2 with an 11.20 ERA in his last three starts before Saturday night.