Updated

Rain in the D.C. area forced the Washington Nationals and Los Angeles Dodgers to play a day-night doubleheader Wednesday at Nationals Park.

Last night's opener of a three-game series was postponed due to torrential downpours.

The Nationals are closing in on their first postseason berth since 1981, but will have to get through the playoff-hopeful Dodgers, who are just 1 1/2 games behind St. Louis for the last of two wild card berths in the National League.

Washington, which is 5 1/2 games ahead of Atlanta for the NL East lead, was swept in three games at Atlanta over the weekend and dropped a 5-1 decision Sunday, as Gio Gonzalez failed in his attempt for win No. 20 and yielded two runs in five innings.

"I wasn't pounding the strike zone," Gonzalez said. "I was nipping at corners, trying to be too perfect."

Ian Desmond had two hits and an RBI for the Nationals, who have lost five of nine games and got two hits from Ryan Zimmerman.

The Nationals also will host Milwaukee for four games on their homestand. They will have outfielder Michael Morse back in the lineup today after he missed the past four games with a wrist and thumb injury.

Taking the ball for the hosts tonight will be Jordan Zimmermann. Zimmermann did not record a decision in a 5-3 win against the New York Mets last Tuesday and was reached for a pair of runs in five innings.

Zimmermann, a right-hander, is 10-8 with a 3.01 earned run average in 29 starts this season. He did not record a decision in his only appearance against the Dodgers, allowing six runs in six innings.

Los Angeles sits one game behind the St. Louis Cardinals for the final postseason spot in the NL and will begin a nine-game road trip tonight against the Nationals, Reds and Padres.

The Dodgers split a four-game set with St. Louis, but dropped a 5-2 decision in 12 innings on Sunday. John Ely was charged with all three runs in the top of the 12th inning to suffer the loss and Stephen Fife tossed the first five innings, allowing two runs and four hits with nine strikeouts.

"We had opportunities ... we just couldn't do it," Dodgers manager Don Mattingly said.

Andre Ethier hit a two-run homer and Hanley Ramirez ended with a team-best two hits for the Dodgers, who have dropped eight of 11 games.

Aaron Harang gets the start for the Dodgers tonight and is 0-2 in his past four trips to the mound. Harang was beaten by Arizona the last time out in a 3-2 defeat on Wednesday and surrendered three runs in 5 2/3 innings to fall to 9-9 in 28 starts this season to go along with a 3.79 ERA.

The right-handed Harang has made seven career starts against the Nationals and is 1-2 with a 3.89 ERA in that span.

Josh Beckett draws the nod for L.A. in the nightcap and is 1-2 with a 3.38 ERA in four starts with his new club. Acquired in a trade from Boston, Beckett did not record a decision his last time out in a 2-1 loss against the Cardinals and hurled 5 1/3 innings of one-run ball. The right-hander, who was 5-11 in 21 starts with the Red Sox, is 7-2 with a 2.37 ERA in 16 career games (15 starts) against the Nationals.

Opposing Beckett will be John Lannan. Lannan, who has been Washington's Opening Day starter on two occasions, has won all three of his starts since coming up from the minor leagues. The southpaw is coming off 5 2/3 shutout innings in a 2-0 road win against the New York Mets.

Lannan has made five career starts against the Dodgers, going 4-1 with a 2.64 ERA.

Los Angeles swept a three-game series from Washington back in late April and has won the previous five meetings between the clubs.