SEATTLE — If the obituary of this unexpectedly successful season for the Mariners is written before the season ends Oct. 3, an annual rite that has usually occurred in early- to-mid-August than mid-September, there will be an assortment of reasons for its ultimate demise without a postseason appearance.

From the misguided offseason rant of an executive that forced his resignation to the rash of injuries, to an offense that was barely anemic on its worst days and inconsistent on its best, there will be no shortage of blame for yet another season — 20 in a row to be exact — without making the playoffs.

But the failures of the Mariners in two critical home series against inferior teams will loom as unwanted memories.

Jarred Kelenic's massive two-run homer into the open seating of the "Hit It Here Café" on the second deck of right field wasn't quite enough to overcome a three-run, no-out implosion from reliever Anthony Misiewicz in the sixth inning and a tack-on homer allowed by Erik Swanson in the seventh, which led to a disappointing 5-4 loss to the Arizona Diamondbacks.

The defeat ruined an otherwise perfect Sunday afternoon at T-Mobile Park where a crowd of only 13,551 watched the Mariners lose a three-game series to the worst team in the National League at 47-96. A week ago, the Mariners swept Arizona in Phoenix and returned to Seattle a few day later just one game back in the wild race.

If this seems familiar, the Mariners dropped three of four to the Royals in August late August after returning from a road trip a game from the second wild-card spot.

The Mariners (77-66) fell to three games back for the second wild-card spot. The Blue Jays improved to 80-63, moved into a tie with the Red Sox, who lost on a walk-off hit in Chicago to fall to 81-64, for the top wild-card spot. The A's have also dropped to three back, losing a series to the lowly Rangers.

The Yankees still sit ahead of the Mariners in the wild card race.

All is not lost for the Mariners as they open a huge three-game series vs. Boston on Monday. It's their last time to face a team directly ahead of them in the wild-card standings.

Still, this lost series could have lasting repercussions as the number of games remaining is down to 19.

Misiewicz entered the game to start the sixth inning after starter Yusei Kikuchi gave the Mariners a workable start.

With multiple left-handers scheduled to hit for Arizona, the pocket of hitters fit for the oft-used lefty reliever. But he never recorded an out, allowing a single, a double, a two-run double and another RBI single that turned a 1-1 game into a 4-1 deficit.

Kikuchi pitched five innings, allowing one run on six hits with a walk and eight strikeouts. It was certainly an improvement over his previous outing, a 1 2/3-inning dumpster fire in Houston where he couldn't throw a strike with his fastball and the game was lost in a six-run second inning.

There would be no repeat of those struggles, but Kikuchi wasn't dominant either. After striking out four of the first six batters he faced, he allowed a leadoff double to Seth Beer to start the third. It eventually led to a run on an RBI single from Josh Van Meter. Arizona loaded the bases with one out in the fourth inning, but Kikuchi worked out of the jam, striking out Henry Ramos and Beer.