On Saturday, Chris Nelson's bases-loaded walk forced in the go-ahead run in the 13th inning and Colorado snapped a nine-game skid by topping Houston, 4-2.
Jordan Lyles (2-8) walked Thomas Field to start the frame, then Field moved to third on Astros catcher Humberto Quintero's fielding error on an Eric Young dribbler. Dexter Fowler was given a free pass with one out, and Nelson worked a base on balls to force in Field.
Aneury Rodriguez came on but served up a sacrifice fly to pinch-hitter Wilin Rosario and Colorado led by two.
Rafael Betancourt retired the side in order for his seventh save. It made a winner of Matt Reynolds (1-2), who walked two but turned in a scoreless 12th.
Jordan Pacheco hit a two-run double for the Rockies, who hadn't tasted victory since September 14 at Milwaukee.
"We did a great job of hanging in there," said Rockies manager Jim Tracy. "Once again, it goes back to the opportunities that we had, and that we finally came through."
Brett Wallace clubbed a solo homer for the Astros.
"I've really tried to focus on adjustments, and being ready for when I get my opportunities," said Wallace of his successful at-bats since his return from the minors.
Millwood, who's appeared in 422 games since being drafted by the Atlanta Braves in 1993, took an 8-2 loss to San Diego in his last start on Sept. 19. The 36-year-old was roughed up for nine hits and seven runs in just 3 1/3 innings.
He's made eight big-league starts since signing with the Rockies and has given up 25 runs in 55 hits in 47 1/3 innings.
Millwood is 7-4 in 12 career starts against the Astros.
For Houston, second-year righty Lucas Harrell makes the fifth start of his big-league career.
Harrell, who was 14 when Millwood debuted in 1999, was 1-0 in eight games with the Chicago White Sox as a rookie in 2010, allowing 13 earned runs in 24 innings.
He made three appearances for the White Sox this season with a 7.20 earned run average before being placed on waivers and claimed by the Astros on July 8.
In four appearances -- one start -- with Houston, he's given up five hits and two earned runs in nine innings.
Harrell has never faced the Rockies.
The Rockies swept a three-game set at home over the Astros from Aug. 22-24, but Houston has won seven of the past 10 as the host in this series.