With the game tied at 3, Adam Kennedy led off the seventh with a single off Jordan Norberto (0-2). He advanced to second on pinch hitter Alberto Gonzalez's sacrifice bunt and, after Roger Bernadina popped out, Desmond singled to right for the lead.
The hit broke a scoreless streak of 17 2-3 innings by the Diamondbacks bullpen.
Washington's Stephen Strasburg, coming off the shortest start of his brief career, departed after five innings with the game tied at 3. His throwing error in the second led to two unearned runs in the Arizona second.
The right-hander allowed three runs — one earned — on five hits, walked none and struck out seven.