Mock dominated the Reds in the first four innings, striking out five batters, and he was able to get out of trouble in his final two frames. With two outs and nobody on in the fifth, Cincinnati starter Aaron Harang hit a routine fly ball to shallow center field.
At first, it looked like shortstop Cristian Guzman was going to make the catch, but it ended up dropping for a base hit. Center fielder Nyjer Morgan said he should have caught the ball.
"I just didn't take charge," Morgan said. "That was my ball. I kind of came out of it [lackadaisically], but I had to keep my head in the game. You just never know when that baseball is going to find you, no matter what."
Morgan made up for his lackadaisical effort two batters later. After Willy Taveras singled to put runners on first and second, Paul Janish singled to center. Harang tried to score on the play, but he was thrown out by Morgan to end the inning.
Morgan said he was not surprised that Harang was sent home by third-base coach Mark Berry.
"It one of those things where I had to stay focused and keep us in the game," Morgan said. "I knew it was going to be one of those plays, because they were really not getting that much offense.
"They were going to try to put a little pressure on us. I made that mistake out there. It's just part of the game where I knew I had to stay focus and get that guy."
In the sixth, Mock showed that he could get out of jams. With Laynce Nix on first and two outs, interim manager Jim Riggleman told Mock to walk Jonny Gomes intentionally. But Mock allowed a free pass to Adam Rosales to load the bases. Riggleman then decided to leave Mock in the game, because the skipper was concerned that the Reds would use a pinch-hitter if he brought in a reliever.
The non-move paid off as Craig Tatum popped up to end the threat.
"It was going to be one thing or the other, depending on who was up," Mock said. "After we intentionally walked Gomes and walked Rosales, I was really glad that [Riggleman] let me stay out there. I did not want to come out of the game. I wanted to finish that inning."
After the game, Mock declined to give himself credit for pitching a great game.
"I had a great game because the defense ... did an unbelievable job," Mock said.
Riggleman was more open about Mock's performance.
"I thought Mock was real good," Riggleman said. "He was good in his last outing. But I thought he was a little better tonight. He was really composed. He made all his pitches. He was sharper. I thought it was his best."
Harang also had a solid outing, giving up two runs in seven innings. However, the Reds righty was hurt by the long ball, as Ronnie Belliard hit a solo home run in the fifth.
"He recognized it," Harang said. "I have a past history with him. He hits me hard or not at all. He's a big free swinger."
Riggleman had a hunch that Belliard might go deep in the game, because the second baseman hit at least five home runs during batting practice a few hours earlier.
"He is on top of his game a little bit right now and doing some good things for us," Riggleman said.
Wil Nieves added another homer two innings later. Like his first career homer, which was hit against the Cubs last season, Nieves hit the second home run of his career over the right-field wall.
"I was looking for something in the middle [of the plate] and [trying to] stay with my approach," Nieves said. "[Harang] threw the ball a little bit up. I got a good swing on it, and it went out of the ballpark."
The victory broke the Nationals' three-game losing streak, improving their record under Riggleman to 15-14.
Bill Ladson is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.