Closer Rafael Soriano allowed the go-ahead, three-run, pinch-hit homer in the ninth inning with two outs to the Giants' Hector Sanchez, and the Nationals lost 4-3.
Soriano said the key call might have been to the previous pitch, when he thought he had a strikeout on a 2-2 call.
"I tried to throw it quarter-in," Soriano said on the home run pitch to Sanchez. "I think it was a bad pitch.
"At the same time, I think when the game be over (was the 2-2 pitch to Sanchez). That pitch I think to me would be a strike. I think that is when the game changed. I think that is when I lost that game. I think to me, that would be the game right there. I don't think it be a bad pitch at all. I think it would be a strike. But I don't make that decision."
Catcher Kurt Suzuki said they were trying to throw a strike on the 3-2 pitch to Sanchez.
"It was 3-2," Suzuki said. "We were trying to throw a strike. Just elevated, it was actually a ball and he hit it. Good piece of hitting by him."
Soriano thought the 2-2 pitch was a strike. Suzuki wasn't so sure.
"That was borderline, could have went either way," Suzuki said. "Probably I thought it was a tick high. Obviously you want guys to swing themselves on base. Nobody is perfect."
Thursday was the third straight game that Soriano was called upon to pitch. Manager Davey Johnson had said before the game he had hoped to give Tyler Clippard and Soriano the day off. They both pitched in the game.
Soriano said he wasn't tired after pitching in every game of the series. He was more disappointed he couldn't get Dan Haren the victory.
"I do it before," Soriano said. "In the past, I do four days in a row. I feel fine. It was just one pitch. I think it would be foul ball, but I see it and see it. He hit it, and that's it.
"I feel fine. I tried to make a good pitch, and the guy hit it. I feel bad because Haren pitched a good game today and, he (gets) a no-decision."
Shortstop Ian Desmond didn't see any fatigue in Soriano despite the three-run homer in the ninth.
"He looks like he always does," Desmond said. "He is under control, he is calm. He has been great. He blew one today. Be ready to go tomorrow."
Desmond instead pointed more to the offense and another game of missed opportunities. The Nationals scored all three of their runs in the third inning, went 2-for-11 with runners in scoring position and left 11 men on base.
"It is tough, but I think probably the bigger story is we had a lot of runners on base and we didn't push them across," Desmond said. "We had the starter out after 3 2/3, and we didn't score after that. We got to do a better job in that game of pushing more runs across."
Twice today, the Giants intentionally walked Suzuki to get to Haren with the bases loaded, and they got him out both times.
"You can't expect Dan to drive in runs in tough situations," Desmond said. "Obviously, he is out there to pitch. There were other opportunities also different guys had opportunities, including myself, and we didn't capitalize. Credit their pitching staff for grinding it out."
Suzuki said the loss hurt because of how close they were to a six-game win streak: one strike and one out away.
"This one was pretty tough," Suzuki said. 'We had him down to one strike, and we really couldn't put the finishing touch on them. They are a good ballclub, keep grinding at bats and fighting and fighting. Fortunately for them, they got one."