Zach McKinstry sacrificed Reks into scoring position, then Mookie Betts ran a 3-1 count before Arizona decided to intentionally walked him.
That set the stage for Muncy, who will start at designated hitter for the National League All-Stars on Tuesday night.
Nobody other than Betts even had a hit until AJ Pollock doubled with one out in the fifth.
“You’d think it carries over automatically, but it just doesn’t work that way,” said Dave Roberts.
Down three runs in the eighth inning, the Dodgers loaded the bases with nobody out with a walk and two singles against Noé Ramirez.
Three leadoff hitters reached base in Gonsolin’s four innings, but the only run came on a solo home run by catcher Stephen Vogt in the fourth.
Gonsolin has also allowed six total runs in his seven games, never more than one in any single game.
“We were fortunate to get him through four innings,” Roberts said.
Despite the high pitch count, there were positives for Gonsolin, who induced a season-high 14 swinging strikes, including five each on his split-change and fastball.
The Diamondbacks piled on in the seventh, when lefty Scott Alexander allowed hits to three of the four left-handed batters he faced, including a two-run home run by second-year catcher/centerfielder Daulton Varsho, who entered Sunday hitting .138/.250/.175 with no home runs.
The next Dodgers game is also in Denver, on Friday against the Rockies , with Julio Urías starting the opener.