Blake Parker (0-1) walked Michael Saunders and Raul Ibanez to open the 10th frame. Jason Bay then cued a sacrifice bunt to third to move the runners into scoring position. Shawn Camp, who replaced Parker, intentionally walked Justin Smoak to load the bases. Zunino worked a full count before ripping the game- winning hit up the middle.
Yoervis Medina (3-2) earned the win after tossing a scoreless 10th inning.
Nick Franklin went 3-for-5 with two doubles and a run scored and Ibanez cracked an RBI triple for the Mariners, winners in three of their last five games. Bay had a solo homer in the victory.
"We had better at-bats as the game went on. Their guy did a good job keeping us off balance, but it was good to see the bats get better later on. That's what we like to see," said Mariners manager Eric Wedge.
Hisashi Iwakuma started for Seattle and gave up four runs on six hits while fanning five over eight innings. Iwakuma has lasted at least seven innings in 10 of his 17 starts this season.
Alfonso Soriano and Dioner Navarro each clubbed solo homers and Ryan Sweeney added an RBI triple for the Cubs, who had won three of four entering the contest.
Cubs starter Travis Wood allowed two runs on three hits over 6 1/3 innings.
"The results were good, but my command tonight was off. I threw a lot of pitches and walked a lot of guys. That just can't happen," Wood said.
The Cubs used a pair of solo shots in the seventh to take a 4-1 lead. Soriano opened the frame with his blast and three batter later Navarro clobbered one over the center-field wall.
Seattle added a run in the home half before plating two in the eighth to tie the game.
In the seventh, Bay walked and Zunino had a base hit two batters later to put runners on the corners. Brad Miller, who made his MLB debut on Friday, then grounded into a force out at second, but it was enough to get Bay across.
Franklin opened the eighth inning with a double then scored on Kendrys Morales' two-bagger to center. Ibanez followed with a triple past a sliding Brian Bogusevic in left field to push the tying run across.
Chicago plated a pair in the second inning to take an early 2-0 lead. Soriano opened the frame with a base hit before coming around on Sweeney's triple to right field. Franklin's relay throw to the plate skipped past Zunino to the backstop, allowing Sweeney to cross the plate.
Bay cracked a solo homer in the fifth to make it 2-1.
Miller had hit safely in 22 straight games for Triple-A Tacoma before getting called up on Friday ... Mariners reliever Oliver Perez has tossed 12 consecutive scoreless innings ... Cubs second baseman Darwin Barney saw his seven-game hitting streak come to an end after going 0-for-4 ... Soriano went 2-for-4 and scored a pair of runs in the setback.
06/29 02:49:56 ET