WASHINGTON -- Adam LaRoche homered with two outs in the bottom of the 11th inning, giving the Washington Nationals their seventh consecutive victory, a 5-4 decision over the Arizona Diamondbacks in the series opener Monday night.

In the top of the 11th, the D-backs loaded the bases with no outs before right-hander Craig Stammen (3-4) struck out the next two hitters and got pinch hitter Cliff Pennington on a grounder to second.

Right-hander Will Harris (0-3), called up earlier in the day, came on for Arizona and retired the first two Nationals in the 11th before LaRoche hit the first walk-off homer of his career.

The Diamondbacks forced extra innings when Nationals right-hander Tyler Clippard couldn't protect a 4-3 lead in the ninth. Closer Rafael Soriano was used a lot lately, so manager Matt Williams wanted Clippard to try for his second save. It didn't happen because right fielder David Peralta led off with a homer to right, tying the score at 4.

The offenses were quiet for the first six innings until Washington catcher Wilson Ramos (2-for-4) hit a two-run homer off Arizona starter Vidal Nuno in the seventh for a 2-1 lead.

The Diamondbacks answered in the top of the eighth when shortstop Didi Gregorius lined a two-run homer to right field. That ended Washington starter Jordan Zimmermann's night and gave Arizona a 3-2 lead.

Washington (70-53) scored twice in the eighth against right-hander Brad Ziegler. Third baseman Anthony Rendon tied it with an RBI triple, and right fielder Jayson Werth put the Nationals up 4-3 with a sacrifice fly.

Neither team did much in the early going. The Nationals stopped two potential Arizona rallies by turning double plays to end the first and third innings -- the latter coming when Nuno tried to sacrifice, and Washington turned it into a 5-6-4 twin killing.

The D-backs (53-72) finally broke through in the top of the fifth. Left fielder Mark Trumbo (walk) and catcher Miguel Montero (single) reached to put runners on first and second with no outs.

They both moved up on first baseman Jordan Pacheco's sacrifice, and Trumbo scored on third baseman Jake Lamb's sacrifice fly to deep center for the game's first run.

Zimmermann pitched seven innings of three-run ball, while Nuno allowed two runs in seven innings.

Montero finished 3-for-4, and Gregorius contributed two hits for Arizona.

NOTES: RF Jayson Werth returned to the Washington starting lineup for the first time since Aug. 7. He was sidelined, except for brief appearances in three games, by a sprained AC joint in his right shoulder. Werth walked and doubled after coming in late during Sunday's 6-5 victory over the Pirates. ...The Nationals signed OF Nate Schierholtz to a minor league contract and assigned him to Triple-A Syracuse. Schierholtz has played 776 games in the major leagues with the Cubs, Phillies and Giants and is a good pinch hitter (.289 average in 166 career at-bats there). ... The Diamondbacks brought up RHP Will Harris from Triple-A Reno before the game. He was 0-2 with a 9.24 ERA in 12 games with Arizona earlier this season. To make room for Harris, the D-backs optioned RHP Bradin Hagens back to Triple-A Reno. Hagens pitched in his first two major league games recently and had an 0-1 record with a 3.38 ERA.