"I was concentrating on getting ahead on hitters, to make it easier," Ramirez said. "I was very confident."
Washington fell to 1-5 at home this season, and the announced crowd of 19,264 was the smallest at 46,382-capacity RFK Stadium since baseball returned to the capital.
At 13-7, the Reds are off to their best 20-game start since 1994, when they were 14-6.
The 23-year-old Ramirez (1-0) was called up from Triple-A Louisville to make his first appearance for the Reds since a spot start on July 4, 2005. Throwing mostly in the 80s and occasionally showcasing a fastball in the low 90s, the right-hander allowed two runs and six hits -- five singles -- in seven-plus innings.
He walked one and even got his first big-league hit.
Shortstop Royce Clayton said the Nationals were able to study only about 20 pitches of video before facing Ramirez.
"That didn't tell us a heck of a lot," Clayton said.
It was another example of the Nationals struggling against an unheralded pitcher.
While Washington has won games started by Houston's Roy Oswalt and Atlanta's John Smoltz this season, it also managed just three hits over seven innings against Mets rookie Brian Bannister when he earned his first major-league victory April 11.
"We don't seem to be able to handle pitchers we don't know. First-time guys, we seem to struggle with them," Nationals manager Frank Robinson said. "We're just not swinging the bats very well right now."
The Reds, who have won five of six, took a 3-0 lead against Hernandez (1-3) in the opening inning by stringing together four hits, including doubles by Felipe Lopez and Edwin Encarnacion. They were helped by an error on right fielder Jose Guillen, who had trouble picking up the ball when Lopez's hit caromed off a wall.
Hernandez has allowed 12 first-inning runs in five starts.
"The first inning's been tough for him this year," catcher Brian Schneider said. "We just need to nip that in the bud as quick as possible and get that figured out."
"We told [Ramirez], 'We're going to score some runs for you,'" Valentin said. "We told him, 'Just concentrate, make your pitches and locate the ball.'"
Hernandez went seven innings, allowing four runs and eight hits. His ERA actually dropped, from 7.11 to 6.68. Washington has lost eight of his last 10 starts dating to Sept. 1, 2005.
"Everybody's waiting for me to do a better job," said Hernandez, an All-Star who had offseason surgery on his right knee and says it's not hampering him. "Everybody knows I can pitch better. It's difficult for me."
Things began a tad roughly for Ramirez, who was 0-3 in 13 previous appearances in the majors for Cincinnati and Philadelphia.
The first batter he faced, Soriano, singled to center and then tagged up and took second on a flyout and scored on Nick Johnson's
single. But Ramirez set down the next 12 hitters in a row. The Nationals scored again off him in the sixth, but two hits, a walk, and a throwing error on third baseman Encarnacion all added up to a solitary run on Guillen's RBI single.
Ramirez stayed ahead of hitters all night, and left after giving up Soriano's single leading off the eighth on his 94th pitch. Brian Shackelford and Todd Coffey finished that inning, and David Weathers pitched the ninth for his fifth save.
The Nationals left two runners on in the sixth and eighth.
"When you're trying to make up ground," Clayton said, "you can't let those opportunities get away."
Ramirez singled off Hernandez in the seventh. ... Nationals infielder-outfielder Marlon Anderson flied out in the seventh, making him 0-for-11 as a pinch-hitter since getting a hit on Opening Day. ... Ramirez took the roster spot of left-hander Eric Milton, who had knee surgery Monday and went on the 15-day DL. ... Soriano has a hit in 10 straight games.