SEATTLE -- When Steve Cishek finally got his chance, he was right on target.

The Seattle Mariners' closer came out of the dugout and delivered a strike -- this time, with a tub of Gatorade that he dumped over teammate Chris Iannetta's head in celebration.

It was the only action of the day for Cishek, who watched fellow reliever Nick Vincent blow a save in the top of the ninth inning before Iannetta's game-winning homer in the 11th gave the Mariners a 6-5 win over Tampa Bay on Wednesday afternoon.

Iannetta completed a four-hour game, and a Mariners sweep, with his leadoff shot. He hit his third home run of the season to deep center field before getting swarmed at home plate and receiving the bath from Cishek.

"Ideally, you don't want to go to the center part of this park," Iannetta said of his homer, "but I'll take it."

Iannetta hit a 3-2 pitch from Tampa Bay reliever Steve Geltz (0-1) for the Mariners' third consecutive win.

"Getting sunburned at Safeco Field in May and winning a game in extra innings is a pretty good day," Mariners manager Scott Servais said.

Geltz said, "Giving up a walk-off home run never feels good. Losing never feels good. But it hurts a lot more when we battle like that and I lose the game."

Reliever Steve Johnson (1-0) earned his first win as a Mariner after pitching 1 2/3 scoreless innings.

Seattle squandered a 4-0 lead in the sixth and a 5-4 advantage in the ninth.

Tampa Bay's Kevin Kiermaier tied the score 5-5 with a one-out, ninth-inning solo homer. Kiermaier's fourth home run of the season came off Vincent, who was in a save situation for only the second time this season because Cishek was getting the day off.

Mariners designated hitter Nelson Cruz provided the go-ahead RBI with a sacrifice fly in the seventh. Cruz's flyout to left scored Robinson Cano from third to break a 4-4 tie.

Tampa Bay designated hitter Corey Dickerson hit the first grand slam of his career to lead a Rays comeback from an early deficit. Cruz led off the third with a solo homer that put the Mariners ahead 4-0.

At that point, Seattle appeared on its way to a series sweep as starter Taijuan Walker settled into a groove over the first five innings. However, Walker started having some control problems in the sixth, when he loaded the bases before Dickerson hit the first pitch he saw over the left-center-field fence for a grand slam that tied the score 4-4.

"That was a huge home run for us," Rays manager Kevin Cash said. "That jolted the dugout and revived us a bit."

Tampa Bay starter Chris Archer allowed four runs on five hits over five innings while walking four. He struck out five.

Walker gave up four runs on five hits over 5 2/3 innings. He walked three, struck out nine and was cruising -- at one point, he retired 11 consecutive Rays -- before hitting a wall in the sixth.

"The couple of walks that I had (in the sixth), that really hurt me," Walker said. "With a 4-0 lead, I have to get out of that."

Archer got into trouble from the outset. The first hitter he faced, Nori Aoki, singled off him before Archer issued walks to three of the next four batters he faced.

A bases-loaded walk to Kyle Seager drove in Aoki for a 1-0 lead. Seth Smith followed with a bases-loaded single, driving in a pair of runs.

The Cruz homer increased the lead to 4-0 in the third.

Tampa Bay's Brandon Guyer hit a one-out double in the sixth, then Walker issued back-to-back walks to load the bases for Dickerson, who belted his eighth home run of the season.

NOTES: Rays INF Steve Pearce made his second start of the season at second base Wednesday. Pearce has spent most of the season at first base but was filling in while 2B Logan Forsythe recovers from a bruised shoulder. ... Forsythe was out of the starting lineup for a second consecutive day after getting hit by a pitch Monday night. The Rays hope he will be back in action Friday. ... Both the Rays and Mariners have Thursday off. Seattle hosts the Los Angeles Angels on Friday, while Tampa Bay begins a three-game series in Oakland on Friday. ... The Mariners announced their rotation for the upcoming series with Los Angeles, and there are no changes. RHP Nathan Karns is scheduled to be on the mound Friday, followed by RHP Hisashi Iwakuma on Saturday and RHP Felix Hernandez on Sunday. ... Tampa Bay's rotation for the weekend series at Oakland has RHP Jake Odorizzi (Friday), RHP Matt Andriese (Saturday) and LHP Matt Moore (Sunday).