With the victory, Miami took two of three from the Angels and enjoyed its first series win since capturing two of three at San Diego from April 21-23.
Riddle's home run off Matt Shoemaker put the Marlins ahead to stay in a three-run fifth inning.
Miami's regular leadoff batter Dee Gordon was given the day off, and manager Don Mattingly opted for Riddle atop the order in place of eighth, where he has mostly batted.
The decision was made because Shoemaker frequently throws a split-fastball, which gets him plenty of ground balls.
"I think Riddle hits the ball good down in the zone," Mattingly said. "I feel he was a good matchup there today."
In the first inning, Riddle bounced a splitter to second for an out. But in the fifth, after pinch-hitter Ichiro Suzuki's RBI single tied the score at 2, Riddle jumped on Shoemaker's first pitch -- a 90.4-mph two-seam fastball.
The pitch was up in the zone, and Riddle didn't miss it. According to Statcast™, the home run projected at 398 feet with a 103.9-mph exit speed and a 21-degree launch angle.
"I just wanted to see a ball up that at-bat," Riddle said. "The at-bat before that, I was swinging at stuff down. I know he loves the splitter. He got ahead with his heater the first two at-bats. When I saw the ball up, I put a good swing on it."
In the sixth inning, Riddle delivered an opposite-field, RBI double, giving him a three-RBI afternoon.
"I'm a lot more comfortable up here," Riddle said. "Of course, the more at-bats and playing every day helps. You're getting your four or five ABs, so that's huge, getting into a rhythm doing that."
After opening at Triple-A New Orleans, Riddle -- ranked by MLBPipeline.com as Miami's No. 11 prospect -- is now the Marlins' primary shortstop since Adeiny Hechavarria is on the disabled list with a left oblique strain.
Hechavarria is about two weeks from being ready for rehab assignment games, so Riddle is getting plenty of playing time.
The left-handed-hitting shortstop has shown some power with three homers and 13 RBIs.
"It's tough hitting up here, that's for sure," Riddle said. "There's still a lot of season left, and you're going to go through ups and downs. The main thing is being consistent. That was my biggest goal coming through Minor League ball, it's being able to be consistent over a five- or six-month period. That's my main focus. The game is very humbling. You can be in a slump in no time."