Before the game, Rockies manager Jim Tracy said he'd rather be competing for a playoff spot, but he found some excitement in seeing how the new blood flows in Major League games.
Afterward, Tracy found reason to be excited about both. Rosario called and handled what Tracy called Jason Hammel's best start since he joined the Rockies in 2009, and Pacheco had a 2-for-4 evening.
"Rosario did not seem a whole lot fazed by anything," Tracy said. "He had energy back there. He had a presence back there. That's something you're waiting to see when you catch your first big league game. And Pacheco took some great at-bats tonight."
Both also had miscues. Rosario, up from Double-A Tulsa, was charged with a passed ball when he lost concentration after Chris Young squared to bunt a Hammel curveball in the seventh. It led to an unearned run that put the D-backs up, 2-1, in the seventh. Pacheco, who played mostly catcher at Triple-A Colorado Springs, committed a throwing error on Miguel Montero's grounder that allowed a run to score in the top of the eighth.
"This is one game," Tracy said. "There were a couple things that showed up in both cases tonight. If you're interested in being really good on a regular basis, those things don't happen very often.
"There will be little things to work on each and every day. But you've got to realize those type of mistakes are things that you can't ignore."
The Rockies' scrutiny of prospects will continue on Sunday, when left-handed pitcher Drew Pomeranz makes his Major League debut in a start against the Reds at Coors Field.
Rosario, 22, signed out of the Dominican Republic in 2006, will be under the microscope.
Tracy made it a point before the game and afterward to compliment the work of Chris Iannetta, the regular catcher throughout the season. Tracy said that Iannetta has played well, especially defensively, over the last six weeks. But Tracy also said that it's time to look at Rosario, who hit .249 with 15 home runs and 48 RBIs at Tulsa.
He arrived in Denver with confidence.
"It felt like a normal game," Rosario said. "I don't think I'm the first player that's had his first game in the big leagues. I felt comfortable. That's my game.
"Hammel was awesome. I'm very excited because we won and because he pitched very well. I didn't tell him anything different. I only told him to throw the fastball, throw down and trust in the pitch."
Hammel also sees a positive future for Rosario.
"Outstanding, he's a good target," Hammel said. "The sky is the limit for this kid. He's obviously good. I think he's going to be a very welcome asset to this team."
Rockies shortstop Troy Tulowitzki said he likes Rosario's confidence.
"He called a great game, and he wasn't scared," Tulowitzki said. "I've known him for a while, and that's one thing that I've understood about his game. If you call him up at this level, this guy's not going to be scared. He's really fearless. I think he's going to be really good."
Pacheco, 25, a ninth-round selection in the 2007 MLB First-Year Player Draft, hit .278 with 21 doubles, three home runs and 50 RBIs in 97 games at Colorado Springs. He began catching in 2008, but also played several positions at Triple-A.
He could move around with the Rockies, since the team is going to take a long look at Rosario and has to find playing time for Kevin Kouzmanoff and Ty Wigginton at third base.
Pacheco said before the game that he was surprised he was in the lineup, but he delivered in the spotlight.
"He had one boo-boo with a throw that would have gotten us out of the eighth inning," Tracy said. "But it's not like he's played third base every single day for an entire season, either. He's not afraid to work. We'll get things straightened out there. Not a problem."
The Rockies also activated Minor League veteran reliever Jim Miller, whose only previous Major League action was eight games with the Orioles in 2008.