Denver, CO -- (Sports Network) - Todd Helton went 2-for-4 and knocked in two runs, as the Colorado Rockies upended the Chicago Cubs, 6-2, in the opener of a four-game series at Coors Field.

Chris Iannetta hit a two-run homer, and Brad Hawpe added a two-run single for the Rockies, who have won six of their last eight games. Ubaldo Jimenez (9-9) gave up two runs -- one earned -- on four hits over 6 2/3 innings to get the win. He also walked five and struck out six.

"It's important, each of these games," said Colorado shortstop Troy Tulowitzki. "The Cubs are right there with us, and it was nice to get off to a good start."

Alfonso Soriano finished 2-for-4 with an RBI for the Cubs, who have dropped three of five and slipped a game behind St. Louis for first place in the NL Central standings. The Cardinals defeated Pittsburgh, 6-4.

Carlos Zambrano was scheduled to start for Chicago but was scratched because of lower back stiffness. The same ailment forced the right-hander to leave his last appearance on Saturday after three innings. He is scheduled to undergo an MRI Saturday in Chicago.

"He went out there to warm up, and he said that after two or three pitches, his back tightened up and he started getting spasms," said Cubs manager Lou Piniella.

Lefty Sean Marshall (3-7) replaced Zambrano on the mound and yielded three runs and five hits in two innings of work. Jeff Samardzija tossed four innings of relief and surrendered the home run to Iannetta.

Kosuke Fukudome walked to begin the ballgame, scampered to third on a Milton Bradley single and scored when Derrek Lee grounded into a 6-4-3 double play.

Colorado quickly countered with three runs in the bottom of the first inning. Carlos Gonzalez ripped a one-out double, and Helton tied the game with a base hit to center. A double by Tulowitzki put two men in scoring position for Hawpe, who slapped a single to right for a 3-1 lead.

Iannetta blasted a two-run homer in the fourth, but Chicago got a run back in the sixth on a broken-bat single by Soriano.

The Rockies widened the gap in the seventh, when Gonzalez led off with a triple and Helton lined an RBI single to center.

Game Notes

Helton has hit safely in 12 straight games...Dexter Fowler collected three hits for Colorado...The Rockies have won 15 straight games against the NL Central...The Cubs activated catcher Geovany Soto from the 15-day disabled list and optioned infielder/outfielder Micah Hoffpauir to Triple-A Iowa. Soto went 0-for-4 in the game.