Nationals 4, Red Sox 3: Roger Bernadina drove in rookie Bryce Harper with the go-ahead run in the ninth inning as visiting Washington completed a three-game sweep at Fenway Park.

Danny Espinosa added two RBIs and Jordan Zimmermann pitched seven strong innings for the Nationals, who have won five of six.

Harper pinch hit for Tyler Moore with one out in the ninth and drew a walk against Alfredo Aceves (0-4). Jesus Flores struck out but Bernadina followed and ripped a shot down the right field line. Harper was running on the pitch and scored easily from first.

Tom Gorzelanny (2-1) got the win in relief and Tyler Clippard worked the ninth for his third save in as many days and eighth of the season.

Boston has lost five of six and remains in last place in the American League East, two games below .500 (29-31).

The Red Sox grabbed a 2-1 lead on David Ortiz’s solo blast in the fourth - his 14th - and Jon Lester was cruising along until the seventh, when Washington jumped back on top.

Ian Desmond and Moore led off with back-to-back singles and moved up on a double steal. Lester struck out Flores and got Bernadina to pop an attempted squeeze bunt out to third but failed to escape the jam, when Espinosa sent a two-run double to left.

Zimmermann failed to hold the slim lead in the bottom of the frame, also allowing back-to-back leadoff singles. Boston ended up tying it at 3-3 on Scott Podsednik’s RBI groundout.

GAME NOTEBOOK: The Red Sox recalled right-hander Mark Melancon from Triple-A and placed left-hander Rich Hill on the disabled list. Hill, who underwent Tommy John surgery last season, will visit with Dr. James Andrews. … Boston C Jarrod Saltalamacchia went 0-for-4 with four strikeouts. … Harper was out at the start with a sore back. … Red Sox manager Bobby Valentine was ejected in the bottom of the ninth for arguing balls and strikes.