Center fielder Matt Kemp added three more hits, falling just a double shy of the cycle and reaching the 100-RBI plateau for the first time in his professional career.
And it was Ethier who turned in the defensive gem of the night in the bottom of the eighth inning, throwing out the potential tying run in speedy Willie Harris at home to end the threat and ice the win.
The victory reduces the Dodgers' magic number to sew up a playoff spot to one, but they could not clinch yet as Atlanta, still in the National League Wild Card hunt, had the night off.
Furcal, who was a triple shy of the cycle, collected a single and two doubles to go with his game-winning homer. He also went 4-for-5 in Tuesday's series opener against Washington (52-100).
Kemp's three hits included a three-run homer in the first inning that got the night's scoring started, as well as a third-inning single and a seventh-inning triple. He did reach second in the fifth inning on a hard liner that left fielder Josh Willingham dropped for an error.
Kemp's homer gave him 100 RBIs for the season and kept him on pace to become the first player in franchise history to hit .300 with 25 homers, 100 RBIs and 30 steals. With nine games left, he is hitting .306 with 26 home runs, 100 RBIs and 34 steals.
"We knew what his tools were," Torre of Kemp, who turned 25 on Wednesday. "But to be able to put together what he's put together this year? To me, he's come the furthest of anybody."
Kemp was proud of his accomplishments but is more focused on making sure he's still playing in November.
"I'm on a winning team and we have a really good chance of doing some big things this year, so playing good and winning, everything else is extra," he said. "But the World Series, that's what I'm trying to get, what all of us are trying to get."
While Furcal's numbers may not rival those of Kemp, he has now hit safely in 16 of his past 17 games at a .375 pace and is getting hot at the right time, thanks to a lot of hard work.
"I'm trying to be a little more aggressive, make good contact, and I feel stronger than ever," said Furcal, who is hitting .268 with nine homers and 45 RBIs. "I just try to play hard every day. Sometimes when we lose a game by one or two runs I can't sleep. I'm excited when we win. And if we lose, the four hits don't mean anything."
The Dodgers (92-61) squandered an early 4-0 first-inning lead as the Nationals, who refused to make it easy, rallied for three runs in the bottom of the second inning, keyed by RBI hits from Elijah Dukes and Alberto Gonzalez.
The teams traded runs over the next few innings with the Dodgers clinging to a 6-4 lead heading into the bottom of the sixth before the Nationals tied the score on RBI singles by Cristian Guzman and Harris.
Furcal came through with his clutch homer in the eighth, but the game seemed like it might be headed toward extra innings in the bottom half of that inning when, with the Dodgers clinging to a 7-6 lead with two outs and Harris on second, Ian Desmond singled to right field.
But Ethier's laser throw home to catcher Russell Martin nailed Harris at the plate for the third out of the inning to preserve the lead.
Though Ethier leads the Dodgers with 103 RBIs and is hitting .279 this season, this time it was his turn to help win the game with his arm.
"If you can go up there and make a key play where you can keep of the tying or go-ahead run," he said, "it's the same as going up there and knocking in the winning run."
Torre loved watching the play develop from the dugout, but he wasn't that surprised.
"We know the strength of his arm is pretty incredible," he said. "He made it possible to have that one run hold up."
Ramon Troncoso (5-4) tossed 1 1/3 innings of hitless ball to get the win in relief of starter Vicente Padilla, who allowed four runs on five hits over five innings, while closer Jonathan Broxton came on with a perfect ninth for his 36th save.