Seager jumped on a first-pitch slider from Friedrich and drove it into the right-field seats for a two-run shot in the Mariners' 4-2 loss. It was his 24th homer, with half of those coming against left-handers.
That's an extraordinary feat for the 27-year-old third baseman, who has the most home runs in the Majors by a left-handed hitter off southpaws.
"I think he's come so far in that department," manager Lloyd McClendon said. "He takes a lot of pride in it. They keep throwing them at him and I think he leads the league in home runs off left-handers. He's really come a long way and he's become that complete player that we thought he could become."
Though the Mariners lost, Seager continued a late-season surge that has seen him raise his batting average 20 points to .274 over the past 14 games while hitting .455 with six homers and 17 RBIs.
Seager acknowledged he's taken pride in his progress against lefties this year. In 2014, he hit .241 with four home runs and a .661 OPS against southpaws compared to .283 with 21 homers and an .862 OPS vs. righties.
This year, he's hitting .251 with 12 homers and a .754 OPS against righties and .313 with 12 homers and an .856 OPS against lefties.
"Absolutely," he said. "You want to always be going forward. You want to always be getting better. Being able to swing the bat better on lefties and being able to use the whole field, these are things you try to do to continue to go forward.
"You try to get a better swing as you go. You learn different things and try to get better in all aspects of it. I feel like I've been in a little better position this year with lefties and I've had a little more success."
And Seager, now one shy of his career-high 25 home runs, knows he'll continue seeing a lot of southpaws no matter how well he hits them.
"We see a lot of lefties in our division, starter-wise," he said. "But you saw a lot of lefties last year. It's probably no different than any other year. With our lineup the way it is, there's a good chance me and [Robinson] Cano will see a few lefties."
Greg Johns is a reporter for MLB.com. Follow him on Twitter @GregJohnsMLB, read his Mariners Musings blog, and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.