DENVER -- It started out looking like a typical midsummer game at Coors Field with both teams teeing off like the first frame was extended batting practice. The game was tied at 3 after the first, with the two teams combining for a pair of homers, a pair of doubles, a pair of singles, and a hit batter, setting the stage for a long night.

But, unexpectedly, that's where almost all of the offense stopped. The Rockies’ bullpen set a franchise record for scoreless innings by their bullpen in a nine-inning game and the Astros lost, 4-3, in the opener of a two-game set on Tuesday night.

Colorado was vulnerable, having just lost its ace, southpaw Kyle Freeland, to a dislocated right shoulder, forcing the Rockies to go with a “bullpen day."

“You run into that problem when they're bringing in different guys [every inning],” Houston manager Dusty Baker said. “Usually it doesn't work that often, but it worked today.”

Rockies reliever Jake Bird drew the start and hit Mauricio Dubón with the first pitch of the game. Alex Bregman followed with a run-scoring double, and after two strikeouts, Chas McCormick plated Bregman with a single to center. Yainer Diaz doubled home McCormick to get the Astros off to a 3-0 lead before the Rockies came to bat.

Through the next eight innings and six additional relievers, the Astros couldn’t find another run.

“I can't remember playing a game here when it was 3-0 [early] and you don't get any more,” Baker said. “Usually, there are some crooked innings in the middle here and then toward the end. So that was not a typical Coors Field game, but their pitchers had a lot to say about it.”

Bregman was 2-for-3 with a walk in four trips to the plate against four different pitchers, but he downplayed any advantage a team utilizing a bullpen game might have.

“Every single person in here is prepared for every arm that we face,” Bregman said. “We took some decent swings. Got some balls, maybe just off the end that we could have drove. We just didn't do enough offensively today to get the job done.”

The Rockies struck quickly, scoring three runs on a leadoff single and back-to-back first-frame homers from Kris Bryant and Ryan McMahon. They took the lead in the fourth when Astros starter Hunter Brown hit C.J. Cron to lead off the fourth and rookie Ezequiel Tovar tripled him home with two outs for the decisive run.

Brown ended up going 5 1 /3 innings, allowing all four runs on six hits while striking out seven. He settled down quickly after the first three batters, retiring the next nine in succession.

“I felt like my curveball was a little short in the first inning, so I kind of changed the sight-line with that, which was kind of to be expected up here,” Brown said. “Overall, I felt pretty good about everything I was throwing.”

Baker liked what he saw in Brown’s ability to give his team the length they needed, keeping the Astros within reach throughout his time on the hill.

“He had better command of his fastball,” Baker said of the improvement since Brown’s last start against Seattle, when he was out after 88 pitches across three innings. “Surprisingly, he had real good command of his breaking ball here at this altitude. He threw the ball well.”

Baker didn’t coddle the rookie right-hander, sending him back out for the sixth with 91 pitches already under his belt.

“You can't take them out every time at the fifth, because I'll wear my bullpen out,” Baker said. “This is the time of year when guys have more endurance. I got faith in Hunter. We got to show faith, because we know we're gonna need him down the stretch.”

Brown’s resilient performance would typically be enough for a win at Coors Field, but with the Houston bats coming up short, the Astros ended up on the wrong end.