Wang (2-2) allowed four runs and seven hits in 6 1/3 innings, his longest outing since a stint of 7 1/3 innings on June 10, 2008, that began his previous consecutive wins run.
"I think he's just going to get stronger," Nationals manager Davey Johnson said of Wang, who threw more breaking balls because his sinker wasn't sharp. "From what I've seen, he wasn't tired, and he was still throwing the ball hard."
Morse homered into the right-field seats in the third inning for his 21st shot this season. He also hit a run-scoring double in the first. Zimmerman led off the fifth with his seventh home run.
Ian Desmond singled in two runs in Washington's three-run first. Morse leads the Nationals in batting average (.323) and home runs (21).
"Ever since I've been here, he hasn't had really a bad day," said Johnson, who took over as manager on June 26. "He missed one day and came back hitting ropes the next day. I don't know where we'd be without him. He's been awfully good."
Johnson will consider moving Morse to left field, where he was slated to play before first baseman Adam LaRoche tore his labrum and rotator cuff in May. As long as he brings his bat to the ballpark, he should help the Nationals.
"He's just a good hitter," Johnson said. "He hits the breaking ball, fastball. It doesn't matter what they throw him."
Cincinnati's Mike Leake (10-8) allowed six runs -- five earned -- and five hits in six innings. His streak of five straight quality starts was snapped.
"I felt like I threw the ball pretty good," Leake said. "The balls that they hit out were off the plate, good pitches. I don't know if they had a good plan or what."
Wang, who has never had a hit in the major leagues, helped himself with the bat. After catcher Wilson Ramos doubled in the fourth inning, Wang made contact and moved him to third with a grounder to shortstop.
Drew Storen pitched the ninth inning for his 32nd save in 36 chances.
Wang, who made his fourth start of the season, missed the previous two years after shoulder surgery. His back-to-back victories followed starts in which he allowed six runs in each.
In his third start, Wang allowed one hit in six innings against the Chicago Cubs on Aug. 9 while pitching on five days of rest. Wang had six days off before Tuesday's outing because of a rainout on Sunday and a day off Monday.
The Reds took a 2-0 lead in the first inning, by right fielder Jayson Werth kept them from scoring more. Werth made a sliding catch of a ball hit by Brandon Phillips that sliced toward the right-field line. However, after Jay Bruce singled in a run, Werth couldn't pull in a drive by Ramon Hernandez that fell in for a single and drove in the second run.
But that early lead was gone in a hurry.
"We're not scoring a lot of runs right now," Reds manager Dusty Baker said. "It puts a lot of pressure on the pitcher, so you've really got to pitch and play defense."
Reds shortstop Edgar Renteria left the game in the seventh inning after he strained his left groin while running the bases. He will be re-evaluated on Wednesday. This marked the first meeting of the season between these teams. ... The Reds' Johnny Cueto (8-5, 1.94) will face the Nationals' Ross Detwiler on Wednesday.