Walker, leading the league with a .360 average, hit his 32nd home run just inside the right-field foul pole and raised his bat in triumph as he walked toward first base. He has four multihomer games this season.
The Braves began the day tied with New York for the NL East lead but lost their second straight low-scoring game at Coors Field. Colorado's 3-2 victory Tuesday night marked the fewest runs scored in Denver this season.
"Power and finesse, that's the ballgame today," Atlanta manager Bobby Cox said.
Millwood showed a little of both. Using a live fastball and a good curve, he gave up two hits in eight innings and retired his final 19 batters.
"I wasn't really surprised by the pitches, but I was a little surprised with the outcome only two hits," Millwood said. "It's kind of tough to do that in this park."
"He's really no fun at all from the left side," Walker said of Rocker. "He throws the ball hard, 95 mph or above, and makes this awful grunting noise when he throws, too."
Colorado starter Brian Bohanon, pitching with bone chips in his left elbow, matched Millwood, allowing an RBI single by Andruw Jones in the fourth. He struck out a season-high seven and walked none in eight innings.
"I like outings like this," said Bohanon, who has one win in his last 11 starts. "I expect to go out and do this. I haven't been able to do it. That's been the most frustrating thing this year."
After Bohanon left for pinch-hitter in the eighth, Dave Veres (3-5) walked the bases loaded in the ninth but struck out the side to pick up the victory.
Millwood gave up Walker's first homer in the first inning and settled into a groove after walking Kirt Manwaring with two outs in the second. He struck out five of six hitters in the sixth and seventh and fanned seven overall.
"Milly was on top of his game. It's a shame," Chipper Jones said. "We're getting enough hits to score runs. We're just not getting them at the right time."
It was by far Bohanon's best home performance of the season. He entered the game with a 9.53 ERA at Coors Field, and lowered it to 8.48.
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