SEATTLE -- Shortly after Friday night's game, Taylor Motter dashed back onto the field to watch a fireworks display.

He provided his own in the first inning.

Motter hit a grand slam against his former team as the Seattle Mariners defeated the Tampa Bay Rays 12-4 on Friday night in the opener of a three-game series at Safeco Field.

"That was something to remember," Motter said. "Especially against them."

Motter, filling in at shortstop for the injured Jean Segura, made his major league debut for Tampa Bay last year. The utilityman batted .188 in 33 games for the Rays before being acquired by Seattle in an offseason trade.

"They got rid of me, and to do that against them means everything," Motter said. "I'm going to succeed someplace else and I was glad to give them the chance to see that."

Rays manager Kevin Cash's analysis of Motter's slam?

"He did what hitters are supposed to do on breaking balls that are left up in the (strike) zone," Cash said.

Danny Valencia added a three-run shot in the third inning and matched his career high with five RBIs as the Mariners won for the fifth time in six games.

Valencia opened the scoring with a bases-loaded walk in the first inning.

"When you've got the bases loaded, you're not trying to hit a grand slam," Valencia said.

When reminded that Motter did just that in the following at-bat, Valencia said: "Motter can do it all."

Right-hander Christian Bergman (3-2), backed by the early home runs, pitched six innings for the victory. He allowed two runs on seven hits, with two walks and six strikeouts.

"That's huge to come out and score (five in the first inning)," Bergman said. "That allows me to just focus on making pitches and go after them."

In the bottom of the first, Seattle's Ben Gamel -- in his first game in the leadoff spot -- lined a single to right field off right-hander Jake Odorizzi. Guillermo Heredia then hit a ball to second base that Brad Miller, activated from the 10-day disabled list earlier in the day, misplayed for an error. A Robinson Cano walk loaded the bases with no outs.

After a trip to the mound from pitching coach Jim Hickey, Odorizzi got Nelson Cruz to strike out and Kyle Seager to line out to first base. Valencia drew his bases-loaded walk before Motter hit an 0-2 pitch just over the wall in the left-field corner to make it 5-0.

Cash said the error, which led to five unearned runs, "contributed quite a bit."

"Not in any situation do you want to see a starting pitcher throw 48 pitches in any inning, especially the first," Cash said. "I think it just kind of derailed him."

Valencia extended the lead to 8-0 in the third with a three-run shot that bounced off the top of the wall in left field and into the Tampa Bay bullpen.

That was it for Odorizzi (3-3), who allowed only four hits in 2 1/3 innings but also walked three.

The Rays got back-to-back home runs, both to right field, from Colby Rasmus and Tim Beckham with two outs in the top of the fourth off Bergman.

Kevin Kiermaier added a two-run shot off Seattle reliever James Pazos in the seventh to make it 8-4.

The Mariners scored four times in the bottom of the inning to regain their eight-run advantage.

NOTES: Seattle SS Jean Segura was placed on the 10-day disabled list with a right high-ankle sprain. Segura, who was tied for the American League lead with a .341 batting average, suffered the injury while sliding into second base Thursday against Colorado. ... Tampa Bay 3B Evan Longoria left in the middle of the seventh inning because of neck stiffness. ... The Mariners made several other roster moves Friday. They selected INF Tyler Smith and RHP Tyler Cloyd from Triple-A, optioned RHP Casey Lawrence to Tacoma, transferred RHP Ryan Weber (right biceps strain) to the 60-day DL and designated OF Andrew Aplin for assignment. ... Tampa Bay activated 2B Brad Miller (left abdominal strain) from the 10-day DL and optioned OF Mallex Smith to Triple-A Durham. ... Rays RHP Alex Cobb (4-4, 3.67 ERA) is scheduled to start Saturday night against M's rookie RHP Sam Gaviglio (1-1, 3.50).