Milledge capped a big day with two more hits and Odalis Perez pitched six strong innings to help Washington complete a doubleheader sweep of the Rockies by identical 6-3 scores Thursday.
In the first game, Milledge went 3-for-4 with two homers and a career-high four RBI to back Jason Bergmann's first win in nearly three months.
It was second multihomer game for Milledge, who was 5-for-9 with five RBI in the doubleheader. His other multihomer game came on Sept. 29 last year with the Mets.
Milledge has four homers in his last six games, and the Nationals have won six of seven.
"Today, I got pitches that were in my hot spot," said Milledge, hitting .375 with eight RBI in his last nine games. "To be a great hitter you have to capitalize on those consistently."
The Nationals were 18-37 on the road before taking three of four at Coors Field.
"We're coming out here to win whether we're in contention or not. They know that," Milledge said. "I wouldn't say we're spoilers. We came out and played the game right."
The defending NL champions fell 13 games below .500.
"Their starters outpitched our starters this series," Rockies manager Clint Hurdle said. "We didn't hit in situations when we needed to hit. Combine that and you have the series that we had."
It was the Nationals' first doubleheader sweep since Sept. 2, 2006, against Arizona. The last time the Rockies were swept was Aug. 19, 2004, against the New York Mets.
Joel Hanrahan saved both games of the twinbill, giving him three saves this season.
Perez (5-8) gave up a two-run homer to Garrett Atkins in the first inning before settling down. Meanwhile, the Nationals roughed up Rockies starter Ubaldo Jimenez, who was 6-1 in his previous seven starts.
"It was good for us," Washington manager Manny Acta said. "All year we've been struggling for runs."
Jimenez (8-10) had a 14-inning scoreless streak coming into the nightcap, but that ended in the second. With two outs, Emilio Bonifacio, Willie Harris and Milledge had run-scoring hits that gave the Nationals a 4-2 lead. Wil Nieves made it 6-2 with a two-run double in the fifth.
Bonifacio had four hits in the doubleheader.
Jimenez gave up six runs on eight hits and six walks in five innings.
"I was wild. I didn't have my control," he said. "I don't know why."
- Hurdle said he expects RHP Livan Hernandez to be in uniform Friday. The Rockies acquired Hernandez from Minnesota on Thursday.
- The Nationals franchise and Colorado have played two previous doubleheaders, both in 1999 as a result of the Columbine High School shooting in April of that year. The Nationals, then the Montreal Expos, swept the first doubleheader on Aug. 12, and two days later the Rockies swept a doubleheader from the Expos.