BALTIMORE -- An argument over a called strike nearly ruined Felipe Lopez's chance to win the game.
In this interleague matchup between last-place teams, no lead was safe until Lopez delivered his go-ahead hit.
Ray (3-5) got the first two outs in the 11th before Robert Fick singled. Ray walked the next two batters and went to 1-0 on Lopez, then threw a low pitch that plate umpire Bill Miller called a strike.
Lopez stepped out of the box and disputed the call. Washington manager Manny Acta sprinted from the dugout and first base coach Jerry Morales quickly stepped in, saving Lopez from a possible ejection.
"We only had (backup catcher Jesus) Flores left, and (Ronnie) Belliard was already in the game as the designated hitter," Acta said. "We had to go out there and calm him down, speak a little Spanish with him and keep him cool."
After taking a ball, Lopez hit a sharp grounder down the first-base line that skipped into the right-field corner.
"You don't want him to get thrown out of the game like that, in a big spot," said Washington's Austin Kearns, who had three hits and two RBI.
The victory assured the Nationals a fourth straight series win on the road, a feat the franchise hadn't accomplished in one season since the Montreal Expos did it in 2001. Washington will vie for its second series sweep of the year Thursday night.
Jay Payton had four hits for Baltimore, sending the game into extra innings with the 1,000th of his career. Melvin Mora hit his ninth homer, his second in two nights, but the Orioles lost for the ninth time in 11 games and fell a season-high seven games under .500 (29-36).
"There was some positives to be taken out of the game, no question, but the fact of the matter is we just didn't come out on the winning end of it," Orioles manager Sam Perlozzo said.
Baltimore pitchers walked seven batters, including two in the 11th and two in the eighth, when Washington scored twice to take a 6-5 lead.
"The walks will always kill you," Perlozzo said. "You just can't walk too many people."
Billy Traber (2-0) worked the 10th and Saul Rivera got his third save.
Down 6-5, Baltimore tied it in the ninth against Nationals closer Chad Cordero. Mora drew a leadoff walk and was replaced by Freddie Bynum, who went to second on a two-out infield hit by Aubrey Huff. Payton then blooped a single to center to bring home Bynum.
Washington trailed 5-4 before moving in front in the eighth against Baltimore's struggling bullpen. Todd Williams walked two of three batters before being replaced by Jamie Walker, who retired Dmitri Young on a fly ball.
Chad Bradford entered, and Kearns bounced a single to center before Ryan Church singled to put the Nationals in front.
"We just needed to get three outs in the eighth and couldn't do that," Perlozzo lamented.
Trailing 4-2 in the seventh, Baltimore briefly went ahead with a two-out uprising. After Brian Roberts and Mora struck out, Nick Markakis doubled to chase starter Matt Chico. Jesus Colome walked Miguel Tejada, and Huff greeted Ray King with an RBI single.
Jon Rauch then yielded a two-run double to Payton.
"Give the Orioles credit -- they came back against our bullpen, which is one of our strengths," Acta said. "But at the end, our kids put a bunch of good at-bats together with two outs and nobody on."
Baltimore starter Steve Trachsel gave up four runs and six hits in seven innings. He left with a 5-4 lead, but the bullpen ruined his bid to earn his fifth win in six starts.
The Orioles got an unearned run in the first when Tejada hit an RBI single after a throwing error by third baseman Ryan Zimmerman.
Washington went up 2-1 in the second on run-scoring singles by Church and Brian Schneider. Ryan Langerhans homered in the fifth, but Mora connected in the bottom half to make it 3-2.
Washington added a run in the sixth when Zimmerman tripled and scored on a single by Kearns.
The start of the game was delayed by rain for seven minutes. ... Baltimore has led in its last 20 games, but is 10-10 in that span. ... Orioles LHP Adam Loewen will undergo season-ending elbow surgery on Thursday. Loewen has been on the disabled list since May 4 with a stress fracture in his elbow.