Erick Aybar had an early two-run double before Hunter ended it for the Angels (86-69), who remained two games behind Oakland (88-67) after the other three teams in the AL wild-card race all won earlier in the day.
Pinch hitter Maicer Izturis opened the ninth with a single off Stephen Pryor (3-1) and advanced to third on a wild pitch and Peter Bourjos' bunt. Seattle walked rookie Mike Trout to face Hunter, who coolly stroked a single to center.
Hunter, the 37-year-old outfielder who will be a free agent this winter, has been spectacular down the stretch of his fifth season with the Angels, contributing 23 RBIs in 23 games.
Baltimore (89-67) is a half-game ahead of the Athletics atop the wild-card race, while Tampa Bay (85-70) has won seven straight to stay one game behind the Angels.
Justin Smoak hit his third homer in two games for the Mariners, who have lost seven of nine. Brendan Ryan and Franklin Gutierrez drove in early runs, but Seattle couldn't capitalize on a solid start by Felix Hernandez, who struck out nine.
Ernesto Frieri (4-2) pitched the ninth for the Angels, whose bullpen didn't allow a hit in 3 1-3 innings after C.J. Wilson's departure. With 16 wins in 23 games in September, Los Angeles is 17 games over .500 for the first time since the end of the 2009 season, their last playoff year.
Hernandez pitched six innings of five-hit ball, leaving with a lead before the Angels' seventh-inning rally against reliever Josh Kinney. Hernandez, who is slated to face the Angels again in Seattle next week, is 0-2 in four starts against Los Angeles this season.
Wilson, the Angels' $77.5 million left-hander, had his second straight rocky start in a nightmarish second half of the season. After failing to get out of the third inning against Texas last week, he gave up five hits, three walks and several hard-hit outs to the Mariners after retiring his first six batters on 22 pitches, picking up his 800th career strikeout along the way.
After Aybar staked the Angels to a two-run lead in the second inning, they loaded the bases before Hunter grounded out on the first pitch he saw. Aybar also reached third base in the fourth inning, but Trout's harmless flyout ended it.
Seattle evened it in the third after Wilson walked Casper Wells and Chone Figgins. Smoak put the Mariners ahead in the fourth with a long drive, his team-leading 19th of the season.
Hernandez retired nine straight after Aybar's leadoff single in the fourth, but threw 103 pitches before Kinney replaced him to start the seventh. Chris Iannetta singled with one out, and pinch-runner Bourjos scored from second when Hunter fouled off several pitches before dropping a short single into the outfield.
NOTES: Izturis was 0 for 20 as a pinch-hitter this season before connecting in the ninth. ... The Angels surpassed 3 million fans for the season Wednesday night, reaching the mark for the 10th consecutive year since their only World Series championship. ... Dan Haren starts the Angels' regular-season home finale on Wednesday afternoon against Seattle's Hisashi Iwakuma. ... Chris Iannetta drew a 12-pitch walk from Hernandez in the second inning, fouling off five straight pitches with two strikes. ... RHP Jerome Williams pitched well in relief of Wilson for the second straight start, inducing an inning-ending double play on his first pitch and retiring all four batters he faced.