DENVER (AP) -- The music was muffled and the mood melancholy in the Colorado clubhouse even after one of the Rockies' biggest wins of the young season.
Carlos Gonzalez homered twice and the Rockies became the first team to decipher Josh Collmenter 's tomahawk-throwing style, rallying past Arizona 12-4 on Tuesday, but they lost pitcher Jorge De La Rosa in the opener of the day-night doubleheader.
An hour after the game, the Rockies said an MRI showed a complete tear of the ulnar collateral ligament. That likely means Tommy John -style tendon replacement surgery that would sideline the hard-throwing left-hander for a year.
De La Rosa was the Rockies' top pitcher so far with a 5-2 record and a 3.51 ERA. He was coming off his first career complete game when he got hurt.
"Obviously it would put a damper on it," shortstop Troy Tulowitzki said before learning of the dour diagnosis. "I knew his arm was bothering him but I don't know to the extent."
"I wish him the best," Gonzalez said. "I hope he's OK. I want to see that guy back on the mound because he's one of the aces, one of the most important pitchers that we have on our club."
With Ubaldo Jimenez still searching for his first win, De La Rosa had been the Rockies' best pitcher, and his teammates sensed the gravity of his injury as they awaited word on De La Rosa, who was sent to a hospital for the MRI.
"We're very concerned," said Greg Reynolds , who got the win in relief. "I mean, he's a big part of this team and you keep your fingers crossed."
During the opener, a fan in the outfield seats was injured when he fell from the stairs and landed about 15 or 20 feet below on the concrete. Rockies spokesman Jay Alves cited federal privacy law in declining to give details, saying only, "We're aware of the injury in the outfield. He was transported to a local hospital."
Reynolds (2-0) threw 3 2-3 effective innings, allowing one run and three hits. He was recently called up and set to start Saturday, but was pressed into duty when De La Rosa had to leave the game, which was a makeup from an April 3 snowout.
Collmenter (3-1), the Arizona rookie with the unusual straight overhand delivery, blanked Colorado for three innings to run his scoreless streak to 24 before he gave up solo homers to Gonzalez and Seth Smith in the fourth.
The Rockies figured him out after the first time through the order.
"His delivery is funky, so that's why it's so hard for us to have that rhythm. Hitting is about timing, and when you don't have timing it's hard. And it's hard to recognize his pitches," Gonzalez said. "Coming over his head, it's hard to pick him up. His fastball is not too hard but it looks harder. And then you can see the 87 mph on the scoreboard, but it looks a little bit faster than that because he's mechanics are very slow."
The Rockies began to get to Collmenter once they worked the counts into their favor.
Collmenter allowed five runs, just two earned, and five hits in 4 1-3 innings. He walked two and struck out one in a shaky outing after two solid starts that had the baseball world abuzz.
"I missed a few spots, location was off today," said Collmenter, who refused to place some of the blame on the cool, wet weather. "It wasn't going out there and putting it wherever you wanted, I had to fight it today."
The 25-year-old righty, who says he learned to throw that way playing with tomahawks as a kid, left the game in the fifth with the bases loaded following an error on first baseman Xavier Nady , a single and a walk.
Reliever Kam Mickolio walked Tulowitzki to tie it before allowing Todd Helton 's sacrifice fly and Smith's RBI double that gave Colorado a 5-3 lead.
Coming into the game, Collmenter had allowed two runs in 26 innings, with 15 strikeouts and one walk since being called up from Triple-A Reno.
The D-Backs took a 3-0 lead in the third. De La Rosa had a 1-and-1 count on Chris Young with runners at second and third when he was replaced by Reynolds, who intentionally walked Young.
Nady's chopper handcuffed second baseman Jonathan Herrera as Ryan Roberts scored. Screened by Justin Upton , Tulowitzki couldn't come up with Melvin Mora 's hard groundball that scooted under the shortstop's glove for a two-run single that made it 3-0.
The Rockies pulled to 3-2 in the fourth when Gonzalez hit a 75 mph changeup off the second-deck in right field for his seventh homer and Smith sent a fastball into the left-field seats for his fifth home run.
The Rockies scored five times in the seventh off Aaron Heilman , who gave up an RBI single to Herrera, a two-run triple to Dexter Fowler and a two-run homer to Gonzalez, who sent a changeup into the rock pile in center field for his eighth homer.
NOTES: Gonzalez has three career multihomer games. ... Collmenter set a franchise record with 15 consecutive scoreless innings to begin a career as a starter. ... D-Backs RHP Juan Gutierrez left the game with a sore right shoulder after facing just two hitters in the sixth.
Arnie Stapleton can be reached at http://twitter.com/arniestapleton