PHOENIX -- Catcher Chris Iannetta is on a quiet roll, but every now and then, he makes a loud noise.
Iannetta knocked a two-run homer in a three-run fourth inning to ignite the Rockies' 6-4 victory over the D-backs on Wednesday night at Chase Field in front of 18,803.
The National League West-leading Rockies, who also benefited from seven solid innings from right-hander Jhoulys Chacin, improved to 11-4 on the road -- the best road start in the 19-year-old franchise's history.
In addition, first baseman Todd Helton launched his 534th career double -- which drove in two key runs -- to tie Hall of Famer Lou Gehrig for 30th on the all-time list.
But it was Iannetta's show of strength when it mattered that proved highly significant for a club that has searched for production at the bottom of the batting order.
Iannetta is hitting .188, having battled issues with his swing and pitch selection, but seven of his 12 hits have gone for extra bases. The shot off Barry Enright (1-3) was his fourth homer of the season. The one before that was a three-run shot in a 4-1 victory over the Pirates on Saturday.
"It's just a matter of barreling balls up and being on time, but aside from the mechanical thing, hitting in the eight-hole is maintaining a level of aggression," Iannetta said. "I'm starting to learn how much aggression I need, as opposed to [having] too much or too little at times."
The Rockies have won more often than not despite constantly trying to work around holes in the lineup. For example, just ahead of Iannetta's home run, Ian Stewart doubled to drive in the Rockies' first run. Stewart was making his first start since April 16 and had spent nearly two weeks in the Minors overcoming a slump.
The Rockies have seen power from Stewart before. Same is the case with Iannetta, who manager Jim Tracy said is on an upswing.
"[Iannetta is] as strong as anybody in that clubhouse," Tracy said. "When he gets to the point where he's got some force behind it, this guy's capable of driving the ball, but hitting the ball a long way and hitting home runs for us,"
The game also featured a 2-for-4 performance from Carlos Gonzalez in his return to the No. 3 spot in the batting order. He had hit fifth for three games in an attempt to jump-start after a slow beginning, and the move worked.
The Rockies' big fourth and fifth innings made Wednesday night's result more palatable to Tracy than Tuesday night's 4-3 loss. In that one, the Rockies blew multiple late-inning opportunities, then watched the D-backs' Justin Upton win it with a home run in the eighth.
"We did tonight what we had been doing in the early part of the season -- we got some people on base, and we took a couple of at-bats where we got big hits with people on base," Tracy said.
Iannetta, often given high marks for defense and his handling of pitchers, also threw out Juan Miranda on a steal attempt of second and is 3-for-3 against baserunners this series. But his work with pitchers always comes first.
Actually, Chacin did quite well himself, holding the D-backs to three hits and striking out six. Both runs he allowed came on homers -- Enright's first Major League homer, with one out in the third, and Kelly Johnson's one-out shot in the sixth.
But Chacin's effectiveness diminished in the seventh, when he walked Gerardo Parra and gave up a Josh Wilson single with two out. After Iannetta and pitching coach Bob Apodaca visited the mound, Chacin righted himself, and struck out pinch-hitter Xavier Nady.
"If he hit a homer or something, the game's going to be close," Chacin said. "I did what [Apodaca] told me -- get ahead with the breaking ball and finish him with a fastball up."
Said Iannetta: "At that point a lot of your energy is going. You just try to man up and make a pitch."
Chacin displayed outstanding secondary pitches, and showed enough fastball command to keep the D-backs honest.
"He's got four pitches, smooth motion, same delivery, same arm slot, he's around the zone and he can throw them all for strikes," Johnson said. "He gets you in between. He throws just hard enough and doesn't really miss over the middle of the plate very often."
Huston Street replaced Matt Reynolds with one on in the ninth and earned his 11th save in as many opportunities, but not without some drama. Melvin Mora singled in a run, and Chris Young singled to bring the potential go-ahead run to the plate with two out, but Street struck out Johnson swinging.