Pacheco, Wilin Rosario and Chris Nelson had two hits apiece for the Rockies, who had 12 hits in their final home game of 2012.
Rafael Betancourt relieved after a run was in and there with two on and none out in the ninth. He gave up a run-scoring double to Alfonso Soriano before finishing for his 31st save.
Anthony Rizzo homered and had three hits and Luis Valbuena also had two hits for the Cubs, who have lost five straight and nine of 10.
The Cubs (59-97) are on pace to surpass 100 losses for the first time since 1966.
Chicago trailed 7-3 in
Betancourt struck out Starlin Castro and Josh Vitters and got Anthony Recker to ground out to end the game.
It was the eighth consecutive game the Rockies had 10 or more hits. They hit .305 at Coors Field this season to become the first team to hit more than .300 at home since the Yankees and Angels did it in 2007.
For the last six weeks Colorado's offense has been fueled by youth. Thursday's starting lineup featured six rookies and only one player—Nelson—who was in the opening-day lineup.
Despite that, Colorado jumped
Volstad (3-11) allowed seven runs on 10 hits in three innings.
It was enough for starter Jhoulys Chacin to get his first win since Sept. 1. Chacin (3-5) allowed three runs on seven hits, walked four and struck out two in five innings.
Brett Jackson's RBI single in the second was Chicago's first run in a span of 13 innings.
NOTES: Cubs 2B Darwin Barney extended his errorless streak to 141 games to tie for the major league record. Placido Polanco of the Detroit Tigers did it in 2007. ... SS Troy Tulowitzki (left groin surgery) will play in an instructional league game Sunday and has not ruled out returning this season. Tulowitzki has been out since the end of May. ... Rockies OF Dexter Fowler was scheduled to undergo an MRI on his strained left wrist Thursday. ... Colorado drew more than 2.6 million fans for the third straight season despite posting its fewest home wins (35) in a full season.