WASHINGTON — The beleaguered Mets bullpen finally saved one for Johan Santana, preserving a 4-3 victory last night that extended the Washington Nationals’ losing streak to six games.

The Mets snapped an eighth-inning tie when Damion Easley was hit by Saul Rivera’s two-strike pitch with the bases loaded and handed a slim lead to a shaky relief corps that has struggled badly without injured closer Billy Wagner.

But this time, Joe Smith and Pedro Feliciano each worked a scoreless inning to lock down Santana’s elusive 10th win. Feliciano, normally a left-handed specialist, struck out two in a perfect ninth for his third major league save. The other two came last year.

Six times this season New York’s bullpen has cost Santana (10-7) a potential win — with five of the collapses coming in the ninth inning. The two-time AL Cy Young Award winner left with a 3-2 lead in his previous outing last Thursday, only to have San Diego tie it in the ninth.

The relievers also blew a four-run cushion for Pedro Martinez over the last three innings of Monday’s 7-5 loss to Pittsburgh, prompting exasperated manager Jerry Manuel to suggest he might even think about using his starters out of the bullpen if nothing else worked.

Santana rebounded from a tough start to toss seven solid innings. He allowed three runs and eight hits, striking out six and walking two. The left-hander was lifted for a pinch hitter with the bases loaded in the eighth.

David Wright and Carlos Beltran started the inning with consecutive singles, and Fernando Tatis walked to load the bases. Rivera then plunked Easley with a 1-2 pitch that umpires ruled hit him on the helmet.

Washington manager Manny Acta argued vehemently and got all four umps to discuss the play, but the call stood.

Five of the first eight Nationals batters got hits, but Santana gave up just one run and three hits after that to win his third straight decision.