Feliciano led off the ninth by socking a pitch from Juan Gutierrez (0-6) deep into the left-center field gap, making it to third for his first career triple.
After Jose Reyes hit a pop fly for an out, Arizona Manager Kurt Gibson had Gutierrez intentionally walk the bases loaded and brought his outfielders in to play shallow.
But Beltran hit a medium-deep fly to left, easily scoring Feliciano with the winning run.
David Wright drove in three runs on two hits and Angel Pagan went 3-for-4 with two runs scored for the Mets. Closer Francisco Rodriguez (4-2) collected the win by pitching a scoreless top of the ninth.
Justin Upton drove in three runs for Arizona.
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