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SEATTLE -- Kyle Seager made a point during his offseason workout program to get stronger. He didn't expect the work to translate into a 20-homer year in his first full major league season.

Seager became the first Seattle batter since 2009 to hit 20 home runs in a season with a solo shot in the first inning, and the Mariners beat Mike Trout and the Los Angeles Angels 6-1 on Tuesday night.

"It's a nice personal accomplishment. It was a good offseason for me. I worked out really hard, trying to get myself to where you can hit the ball a little harder, and the coaches have helped me out a lot here," Seager said. "... I don't really consider myself a home run hitter."

Seager provided Seattle some early offense, becoming just the fifth player in Mariners history to record a 20-homer season in one of his first two years in the majors. He added a double in the sixth, when the Mariners took a 5-0 lead.

With the Angels out of the playoff chase, much of the attention turned to the Mariners' announcement Tuesday that the fences would be moved in at Safeco Field for the 2013 season, most notably in left-center field, where fly balls notoriously die. Almost on cue, both teams peppered the outfield with fly balls that left question about whether they would be home runs in future seasons.

There was no question about Michael Saunders' two-run double in the fourth inning off Angels starter Dan Haren (12-13) that thudded off the wall on the fly in deep left-center to score John Jaso and Justin Smoak. Seattle's Casper Wells, twice, and the Angels' Hank Conger both hit fly balls that very likely could be homers in future seasons but ended up being flyouts.

"If I was a little stronger, it would have gotten out," Wells said. "Next year it would be a couple of home runs, so that would be cool."

The Mariners are moving in the fences only a few feet in some spots but are making a drastic change in left-center field, which will be shortened by as much as 17 feet in one spot.

Seager reached a power milestone no Seattle batter could in each of the previous two seasons with his homer in the first. Russell Branyan (31) and Jose Lopez (25) in 2009 were the last Seattle hitters to reach the 20-homer mark. With the closer fences, next year should be less celebrated reaching the mark.

"I think it would affect us in a negative way if we really started thinking about it if everyone started trying to hit balls in the air and that kind of deal," Seager said. "If everyone continues with what we've been doing of late, we'll be good."

Hisashi Iwakuma (9-5) made his bid for a spot in Seattle's 2013 plans by winning his third straight start to close the year. He allowed six hits and struck out seven, including Angels slugger Albert Pujols three times, while pitching six scoreless innings. It was just the 12th time in Pujols' career that he struck out three times in a game.

The only two pitchers to strike out Pujols three times in a single game are Iwakuma and Seattle ace Felix Hernandez, who did it less than a week ago in Anaheim.

The Angels left runners at second and third in the first inning, then saw Trout standing at third with no outs in the third and failed to get him home. Iwakuma struck out Howie Kendrick and Pujols and got a groundout from Kendrys Morales to escape the jam.

Iwakuma, who will be a free agent after the season, finished 8-4 with a 2.65 ERA after moving into the starting rotation in July.

"He's made that transition back to starting about as good as you can. When you see runners get on base, the way he executes pitches, he's able to slow the game down and work to the situation," Seattle manager Eric Wedge said.

The penultimate game of the season came a night after the Angels were eliminated from the American League wild-card chase. And they played like a team with nothing tangible left to play for, tying their season high with three errors, including a pair in the sixth inning by right fielder Mark Trumbo that helped two runs score.

Trout had one hit in five at-bats to see his average drop to .324. He's seven points behind leader Miguel Cabrera.

Haren tied his career high in losses but got little help from his defense. He struck out eight but also gave up seven hits and dropped his final two decisions of the season.

"We just couldn't get that hit early that would've helped Dan relax and make some pitches," Angels manager Mike Scioscia said. "On the defensive side, we cracked the door open for them too often."

Game notes

Kendrick had an RBI single in the ninth to score Andrew Romine and avoid the shutout. ... The last time Pujols had two three-strikeout games in a season was 2008. ... Seattle CF Franklin Gutierrez, bothered by a sore groin, did not play Tuesday and won't in the season finale Wednesday.