Bruce took his normal spot in right field, while Duvall replaced the Rockies' Carlos Gonzalez in left.
It didn't take long for Duvall to see game action -- he fielded a Manny Machado flyout at the warning track in what wound up a 1-2-3 inning for Julio Teheran.
Duvall made another heads-up play in the seventh, scooping up a Josh Donaldson popup in shallow left field and relaying to catcher Jonathan Lucroy to prevent Mark Trumbo from tagging up and scoring from third base.
Duvall and Bruce didn't have much luck at the plate, though. Bruce led off the sixth and struck out on three straight pitches against the Royals reliever Kelvin Herrera, and Duvall bookended the inning with a weak dribbler fielded by catcher Matt Wieters, who threw to Eric Hosmer to record the out.
Bruce batted again in the eighth, against the Yankees' Andrew Miller, and struck out. A batter later, trailing 4-2, with runners on first and second and two out, Duvall drew an uncharacteristic walk on nine pitches to load the bases. The 27-year-old entered the break with more home runs than walks -- and, in fact, was 2.2 percentage points more likely to homer than to walk in the first half of 2016.
Although Cardinals rookie shortstop Aledmys Diaz wound up taking a called third strike against Astros reliever Will Harris to end the NL threat, Duvall was pleased with his performance.
"I just went up there and wanted to compete," Duvall said of his second plate appearance. "That's a tough at-bat, and I ended up working a walk, so it was good."
For Duvall, who began the season with a part-time job in left field and won the job outright from Scott Schebler thanks to his offensive production and fielding prowess, being in San Diego was the biggest privilege of all.
"Just being able to play every day is an honor," Duvall said before taking the field on Tuesday. "And then this [being named an All-Star] on top of that, it's pretty amazing."
Duvall, of course, also appeared in Monday's T-Mobile All-Star Home Run Derby, ousting hometown hero Wil Myers before being bested by former Reds slugger Todd Frazier in the semifinals.
Despite his busy schedule, Duvall feels he's heeded Bruce's advice to absorb the experience.
"I wanted to kind of slow everything down and try to just soak it all in and just enjoy it," Duvall said. "I feel like I've done a pretty good job."