Result: The rookie right-hander is perfect through three innings, throwing just 33 pitches.
Action: On the second round through the order, Stammen gets behind in the count to four of the first five batters.
Result: Dustin Pedroia smokes a double down the left-field line, Kevin Youkilis walks and David Ortiz mashes a three-run home run to center field, which puts the Red Sox in front 3-1.
With Ortiz in a 3-2 count, Stammen threw a changeup, instead of his out pitch, the sinker.
"That was a pretty big mental mistake on my part," Stammen said. "I've got to be able to shake that pitch off and throw what I want to throw."
Stammen rejected the idea that his inability to throw first-pitch strikes got him into trouble, citing a first-pitch home run he gave up later in the game. But when Stammen was tossing the initial pitch over the plate during the first three innings, he looked drastically different from the fourth through sixth frames, when he wasn't.
"I think everybody is [better when they get ahead in the count]," manager Manny Acta said. "Regardless of how good of a hitter you are, when you are 0-1, you're batting average drops a lot. When [Stammen] gets ahead and can sink that ball and use his offspeed stuff, he's pretty effective."
Following an impressive outing in Yankee Stadium last week, and a promising dawn to this start, Stammen struggled once the Red Sox's order had seen him once through.
In the fifth inning, Stammen gave up three more hits and a run. Then after recording one out in the sixth, Ortiz singled away from a defensive shift and catcher Jason Varitek belted a two-run shot into the right-field upper deck to knock Stammen out of the game.
Staked to a 6-1 lead, Red Sox starter Jon Lester did just enough to hold onto an advantage before handing the ball over to his bullpen in the seventh inning ahead 6-3.
Against Red Sox reliever Justin Masterson in the seventh inning, the Nationals threatened. Pinch-hitter Josh Bard doubled and Cristian Guzman scorched an RBI triple for his seventh consecutive multihit game.
More importantly, the hit sent the game-tying run in Ryan Zimmerman to the plate. Zimmerman charged the pitch to deep left-center field, where speedy Jacoby Ellsbury scurried over to corral the ball with his back against the wall.
"I thought it had a chance," Zimmerman said. "[The pitch] got in on me a little bit. I guess it was close, but it's just a flyout."
"From my seat, every ball we hit like that has a chance to go out," said Acta. "I guess that's wishful thinking. All of us thought we had it; it would have been very nice."
The Nationals had another chance with two outs in the eighth inning. Elijah Dukes and pinch-hittter Adam Dunn both walked to put the tying run on base. But another pinch-hitter, Ronnie Belliard, struck out swinging to terminate an eight-pitch at-bat against Hideki Okajima.
There was no rally looming in the ninth for the Nationals. Not with Boston closer Jonathan Papelbon setting them down in order for Washington's third loss in a row, following its season-best four-game win streak.
"When you play against a team in that category, you have to play perfect baseball," Acta said. "And today, one pitch basically cost us the game."
Mark Selig is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.