Tyler Clippard threw one too many fastballs Thursday night and he knew it.
The All-Star reliever gave up a two-run double to pinch-hitter Mark Kotsay in the eighth inning that lifted the San Diego Padres to a 2-1 victory over the Washington Nationals.
"I kind of had a mental lapse out there tonight," Clippard said. "On Tuesday, I got him out in a long at-bat with changeups and I felt he might be sitting on that pitch tonight."
With the Padres trailing 1-0, Orlando Hudson drew a one-out walk and Cameron Maybin dropped down a bunt single against Clippard (1-2). Kotsay followed with a double to right-center to put San Diego ahead.
"Tonight I more or less second-guessed myself," said Clippard, who fell behind in the count 2-1 and threw four fastballs. "I've said all along I have to stick to my strength to be successful. It was just poorly executed and the pitching selection wasn't good, either. It was kind of frustrating on my part."
The NL East-leading Nationals (14-5) had won four straight and eight of 10. The franchise was looking for its first sweep in San Diego since the Montreal Expos accomplished the feat in July 1994.
Andrew Cashner (1-1) pitched a perfect eighth and Huston Street earned his second save. Three pitchers combined on a four-hitter for San Diego, which improved to 6-14 and averted a three-game sweep.
"We talked about what a difference one hit would make in a lot of games and tonight you saw it," Padres manager Bud Black said. "We had some opportunities in the game and we didn't get that hit until then."
Kotsay pinch-hit against Clippard in the seventh inning Tuesday night with runners on second and third and one out in a 2-1 game. Kotsay saw 12 pitches in that at-bat and fouled off seven before finally popping out.
"I missed a few pitches I felt I could have put in play Tuesday," Kotsay said. "Even though it was a great at-bat from the perspective that I battled, I was still disappointed with the result. Tonight I got ahead in the count and I told myself to get my sights up because he throws a lot of fastballs up."
Jayson Werth's home run with one out in the seventh off Padres starter Edinson Volquez snapped a scoreless tie. It was Werth's second of the season.
The Padres, who left 11 runners on base, had starter Edwin Jackson in trouble in the fourth when Nick Hundley singled and Yonder Alonso doubled to open the inning. But Jackson struck out Hudson before an intentional walk to Maybin. The right-hander then struck out Jason Bartlett and got Volquez to ground out.
In the sixth, Hudson tripled with two outs but was stranded when Jackson got Maybin to ground out to first baseman Adam LaRoche, who flipped the ball with his glove to Jackson for the out at first.
"I got some timely strikeouts and they made some great plays behind me," Jackson said.
In the seventh, the Padres loaded the bases with two outs, but Clippard struck out Hundley to end the inning.
"These are the types of games we have been winning," Clippard said. "We had the lead late and I felt strong, but I didn't get the job done."
Jackson allowed six hits in 6 2-3 shutout innings. He struck out six and walked three. Nationals pitchers have eight scoreless starts in 19 games this season.
Volquez went seven innings, giving up a run and three hits while walking one and striking out seven.
NOTES: Nationals manager Davey Johnson said 3B Ryan Zimmerman will see a doctor in Los Angeles on Friday to have his ailing right shoulder examined. Johnson said Zimmerman, out since last Saturday, was "not able to swing the bat" on Thursday and would be examined and perhaps receive treatment. Johnson said a determination on whether Zimmerman will go on the disabled list would be made after his visit with the doctor. An MRI showed no structural damage. ... Washington LHP Ross Detwiler (2-0, 0.56 ERA) will open the series at Dodger Stadium on Friday night against LHP Clayton Kershaw (1-0, 1.66), last year's NL Cy Young Award winner.