New York lost its fourth in a row and fell to 3-5 on a 10-game western road trip that will conclude with games against the Angels on Saturday and Sunday.
Iannetta's RBI gave the Angels a 3-2 lead and Mike Trout added RBI singles in both the seventh and eighth innings to back up the five-hit effort from C.J. Wilson.
Wilson (5-5) allowed both New York runs over seven innings, walking three and striking out four. It was only the second win for Wilson in his last eight starts.
Ernesto Frieri came on to strike out two in the ninth for his 15th save.
Andy Pettitte (5-4) gave up a season-high 11 hits and four runs over seven innings to take the loss. The setback came in his first start after recording the 250th victory of his career, which came against Seattle last Saturday.