Singer is in his first season with Cincinnati after he was acquired in a November trade with Kansas City.
Taylor Rogers, Graham Ashcraft and Emilio Pagán followed Singer with four innings of two-hit ball. Pagán handled the ninth for his third save.
Adam Frazier hit a two-run homer for Pittsburgh, and Tommy Pham had an RBI double. Bailey Falter (0-2) was charged with five runs — three earned — and three hits in five innings.
Candelario's first homer made it 3-0 in the first. A two-run throwing error by catcher Endy Rodríguez extended the lead to 5-0 in the third.
Rodríguez entered the game after Joey Bart departed because of lower-back discomfort.
Both teams managed only four hits and combined for 10 walks.
Pittsburgh outfielder Oneil Cruz missed his second consecutive start with a finger injury on his left hand.
Reds outfielder Austin Hays was 0 for 2 with a sacrifice fly in his first rehab start at Triple-A Louisville on Friday night. Hays, who signed as a free agent in the offseason, suffered a left calf injury late in spring training.
Key moment
Rodríguez blocked a wild pitch, but overthrew third trying to get Elly De La Cruz, who scored along with Spencer Steer.
Key stat
The Reds have scored 30 runs in Singer’s three starts.
Up next
Andrew Heaney (0-0, 1.50 ERA) starts for the Pirates on Saturday against fellow left-hander Andrew Abbott, making his season debut after a couple of rehab starts at Triple-A Louisville.
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