Werth hit his 16th homer with two outs in the first. The Dodgers then got a two-out homer in the bottom half from Matt Kemp to take a 2-1 lead.
Asdrubal Cabrera tied it at 2 with a leadoff drive in the third. One batter later, Span hit his first homer of the game.
It was Span's second career multihomer game. His first came on Sept. 13, 2008. His three RBIs were a season high. He is batting .360 in 43 games since the All-Star break.
The outfielder was 2 for 4 with two runs scored and the two-run homer, his 17th of the season. He has 10 RBIs in his last nine games, batting .361 since Aug. 22. His 174 career homers are three behind Mike Piazza for fourth on the Dodgers' career list.
Nationals: 1B Adam LaRoche left in the fifth after straining his lower back during an at-bat. He is day to day. ... OF Steven Souza Jr. (left shoulder) returned from rehab and was reinstated to the active roster. He was named International League MVP last week, having led the league in nearly every offensive category.
Dodgers: RHP Chris Perez (bone spurs, right ankle) was reinstated from the 15-day DL after making five rehab appearances with Single-A Rancho Cucamonga. INF Carlos Triunfel was designated for assignment.
Nationals: With rosters expanding Monday, Washington recalled RHP Aaron Barrett, LHP Xavier Cedeno, C Sandy Leon, INF-OF Tyler Moore and RHP Blake Treinen from Triple-A Syracuse.
Dodgers: Los Angeles recalled C Tim Federowicz, RHP Yimi Garcia, and INF-OF Alex Guerrero from Triple-A Albuquerque and selected the contract of OF Pederson from Albuquerque. Guerrero struck out as a pinch hitter and Garcia made his major league debut in the eighth, allowing one hit and striking out two in two scoreless innings.
Nationals: RHP Doug Fister (12-5, 2.55 ERA) is 0-2 with a 3.86 ERA in his last three starts.
Dodgers: LHP Clayton Kershaw (16-3, 1.73) starts. Among NL pitchers with at least 15 decisions, Kershaw and Fister (.706) rank first and second in winning percentage.