Facing the lowest-scoring team in the American League, Oakland went back to its own low-scoring ways, crossing the plate all of six times in three games.
The Mariners picked on rookie left-hander Gio Gonzalez early and often Wednesday on the way to a 5-3 victory in the finale of a three-game series at Safeco Field.
"It was a frustrating series, very much so, for a lot of reasons," A's manager Bob Geren admitted. "It's frustrating to lose three games when we should have, or could have, won all three."
Oakland's bats were silent in a 3-1 loss Monday; a crucial late error wasted a fine outing by Brett Anderson in the way to a 4-2 loss in 10 innings Tuesday; there was more shoddy defense and more offensive opportunities squandered in the finale.
Oakland designated hitter Jack Cust, who hit his 20th homer and missed by inches what would have been his 21st -- and a game-tying solo shot -- on a video review, summed it all up nicely.
"Kind of a disappointing series," he offered.
Center fielder Rajai Davis was the main defensive culprit on Wednesday. He was unable to catch what he conceded was a ball he could have caught off the bat of former A's DH Mike Sweeney in the first inning, and while that miscue didn't cost the Oakland a run, his two-base error in the seventh inning led to an unearned insurance run.
Jose Lopez' deep fly into the left-center gap bounced off the heel of his glove in the seventh, and Sweeney drove in Lopez by muscling a snapped-bat single into left.
"I had a humbling experience," Davis said. "I just messed up. ... I had 'em both. Normally I catch 'em. This wasn't a normal day."
The A's made Seattle sweat it out a little when Mark Ellis and Ryan Sweeney slapped consecutive singles to start the top of the ninth, but Mariners closer David Aardsma steadied himself to catch Tommy Everidge and pinch-hitter Nomar Garciaparra looking before getting Adam Kennedy to bounce out to end the game.
"Both teams put on a good show," said Gonzalez, who allowed four runs on seven hits and three walks in five uneven innings. "All three games were close games."
Gonzalez, who entered the game with a 3.06 ERA in his past six starts, was in trouble right away, issuing a one-out walk to former A's infielder Jack Hannahan in front of a home run by Lopez in the bottom of the first inning.
"It was a good down-and-away pitch, but like [A's catcher Kurt Suzuki] said, this is the big leagues," Gonzalez said. "Some pop it up, some go yard."
The Mariners made it 3-0 an inning later, though, when Hannahan led off with a double and scored on a single by Bill Hall.
Cust's fourth home run in seven games, a solo shot off Seattle starter Luke French, closed the gap in the fourth, but the hosts got that run back in the fifth when Hannahan walked, moved to third on a double by Lopez and scored on a sacrifice fly by Hall.
Hannahan, traded from Oakland to Seattle for a Minor League pitcher in July, also turned in the defensive play of the game, ranging over to the camera well near the A's dugout in the second inning to make a leaning, stumbling catch on a popup by Scott Hairston.
"Hannahan has done such a phenomenal job for us," said Seattle skipper Don Wakamatsu, Oakland's bench coach last season. "Both defensively and offensively."
Suzuki homered to left after Davis' single in the sixth, and Cust skied what he thought was a game-tying homer over the foul pole in right minutes later. But after the umpires huddled and eventually reviewed the play on tape, the original on-field foul call was upheld.
"I thought when I hit it, it was out," Cust said. "It's a hard call. I assume they might have had a couple more angles than I saw on [tape after the game]."
Added Geren: "I knew it was gonna be extremely close. ... They did the right thing. I like that opportunity for them to see it and get it right. I think it's good for the game."
Mychael Urban is a national writer for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.