Then the man filling in for injured shortstop Jean Segura for the immediate future went out and put the hurt on his previous squad, swatting a first-inning grand slam off right-hander Jake Odorizzi to give the Mariners an early 5-0 lead. The Mariners went on to win, 12-4.
The 27-year-old acknowledged afterward that this one was extra special coming against the team that let him go.
"They gave me my chance in baseball, but I'm going to succeed somewhere else and I'm glad to show them that," Motter said. "I knew what I was going to be there and I know what I'm going to be here. Here I'm getting a lot of opportunities now with guys going down.
"I hate to see that. I wish everyone health and wellness and hopefully Segura gets back soon. But to get an opportunity to do that against this team is meaningful."
After getting off to a scorching start with Seattle, Motter had cooled considerably of late, batting just .180 over the past 33 games as his average dropped from .282 to .209. He'd gone 19 games and 56 at-bats without an extra-base hit until Friday, when he drove a 74-mph curveball just over the fence in left to clear the bases.
Motter joins Alex Rodriguez as the only shortstop in franchise history to hit multiple grand slams in a season. Motter has done it twice, while Rodriguez accomplished the feat in 1996 and again in 1999.
Motter figures to be a key element for the upcoming month or so with Segura sidelined. After making the team as a super utility player, the 27-year-old has wound up with more playing time than anyone expected after a series of injuries to Robinson Cano, Kyle Seager and Segura, who already missed 12 games earlier in the year with a strained hamstring.
Motter thus has played in 47 of the team's first 56 games in a variety of roles and started at every position except right field and catcher.
"I never really expected it to happen the way it has," Motter said before Friday's game. "I knew we have Seager, Segura and Cano and they play 150-some games a year. So for it to happen the way it's happened, it's not been a good thing. I'm not happy by any means that this is the way it's happened, but looking at it, I'm getting some playing time and hopefully I can come out here and help them win."
Motter hit just .188 in 33 games as a rookie for the Rays last year, then was traded to Seattle in November in a deal for Minor Leaguers Dalton Kelly, Andrew Kittredge and Dylan Thompson. He hit .282 with five doubles and four homers among his 11 hits in his first 13 games, but had just five doubles and one homer in his next 100 at-bats.
Manager Scott Servais said opposing teams have figured out how to attack Motter by working him more outside, so he needs to use more of the field instead of staying pull happy. But he pulled Odorizzi's curveball over the fence Friday.
"There's an adjustment," Motter said before the game. "But the biggest thing is I've been missing pitches I should be hitting. Earlier in the season, I wasn't missing those pitches. Now the season has moved on and I'm fouling them back or missing them. So it's not really an adjustment, I'm just missing the pitches I should be crushing."
Against Odorizzi, he fouled off five straight pitches before crushing the curveball. And enjoyed it tremendously.
"We talked about it earlier. I keep missing some pitches that I'm not happy about," Motter said afterward. "But I didn't miss that one."