Zunino moved into a tie for the major league lead in home runs by a catcher with his 18th of the season. Zunino's opposite-field drive to right off Jose Quintana in the fifth gave Seattle a 3-1 lead and came after Chicago third baseman Conor Gillaspie dropped a popup from Logan Morrison. Kendrys Morales added a sacrifice fly later in the inning.
Iwakuma (10-6) became the third Seattle pitcher with double-digit victories this season. The Japanese right-hander allowed one run and five hits, struck out three and walked none.
Iwakuma improved to 5-2 with a 2.04 ERA in his last eight starts. He has pitched at least seven innings in his last seven outings.
Fernando Rodney pitched the ninth for his 32nd save in 35 opportunities as Seattle remained a half-game behind Kansas City for the second wild card in the American League.
Dayan Viciedo continued his success against Seattle with an opposite-field solo homer on the first pitch he saw from Iwakuma in the fourth, but that accounted for all of Chicago's offense. The White Sox have lost four straight and six of seven.
Quintana (6-8) retired 12 of his first 14 batters before falling apart in the fifth when Seattle sent nine batters to the plate. Chris Denorfia walked on four pitches to start the inning, followed by Gillaspie's error. Quintana fell behind Zunino 2-0 and left a fastball elevated on the outer half of the plate.
Quintana followed by giving up singles to Chris Taylor and Austin Jackson, and an intentional walk to Robinson Cano loaded the bases. Morales' fly ball was deep enough for Taylor to score.
Chicago: Outfielder Adam Eaton lasted one batter before leaving the game. Eaton grounded out to start the game and walked slowly back to the dugout. He left with soreness in his rib cage and was replaced by Leury Garcia.
Seattle: Utilityman Willie Bloomquist was lost for the season after a scope on Friday revealed that he needed microfracture surgery on his right knee. Bloomquist should be ready by spring training next season. Bloomquist had played six different field positions this season, but manager Lloyd McClendon said he doesn't feel he needs a true utility player in the short term.
Chicago: Former Seattle pitcher Hector Noesi (6-8) will throw for the second time in his career against the Mariners. Noesi was designated for assignment earlier this season by Seattle, but has latched on with the White Sox and is scheduled to make his 19th start.
Seattle: Left-hander James Paxton (2-0) will make his second start after several setbacks that have limited him this season. Paxton threw 4 1-3 innings on Aug. 2 in Baltimore in his first start since April 8. Paxton first landed on the disabled list in April because of a strained lat muscle.