The Orioles pushed the game past regulation when Chris Davis knocked in two runs in the ninth inning, and the bullpens took over until Seattle's finally blinked in the 18th.
It remained tied until Taylor Teagarden broke the string of eight consecutive scoreless innings with a pinch-hit RBI single, sending Baltimore to its 14th straight win in extra frames.
Tommy Hunter (5-8) stranded a runner in scoring position in both the 16th and 17th innings to earn the win, which moved the Orioles into a tie with the New York Yankees atop the AL East standings.
"That was incredible," said Hunter. "It was a long game, the guys came back, battled and the bullpen did it again."
The Mariners squandered plenty of opportunities to end a two-game skid, going 0-for-17 with runners in scoring position and stranding 16.
"We had so many opportunities, one more hit and the game's over, so it wasn't that we weren't creating opportunities, just nobody stepped up offensively," said Mariners manager Eric Wedge.
Lucas Luetge (2-2), in his second inning of relief, walked Nate McLouth to open the 18th, and a perfect hit-and-run resulted in J.J. Hardy singling through the infield to put runners on the corners.
Teagarden followed with a bloop single down the right-field line to score McLouth, and Hardy crossed the plate with an insurance run on Mark Reynolds' fielder's choice grounder later in the frame.
With very few fans left in the stands, Jim Johnson retired Seattle in order to pick up his league-leading 44th save and end the five-hour, 44-minute affair.
Baltimore has won three straight after dropping two in Oakland.
"It's a really important game," said McLouth. "It's hard to stay locked in for that long. We were lucky to scratch a couple across in the ninth after just a dominant pitching performance by their starter and things worked out our way in the last inning there."
The Mariners left a runner in scoring position in the 10th, 11th, 12th, 15th, 16th and 17th innings.
Miguel Olivo's two-run homer off Wei-Yin Chen in the fourth inning gave the Mariners a 2-0 lead that held up until the ninth.
Erasmo Ramirez cruised through eight innings, allowing just two hits. With a pitch count at 94, Wedge allowed the 22-year-old rookie a shot at finishing off his shutout.
But Ryan Flaherty's pinch-hit single and McLouth's base hit to open the ninth ended Ramirez's bid. With Tom Wilhelmsen on the mound, a sacrifice bunt moved both runners into scoring position, and Davis singled past a diving Dustin Ackley to bring in both runners and tie the game.
Baltimore, which has won seven straight vs. Seattle, improved to 28-8 in one- run games ... Chen, who became the fourth Orioles rookie since 1954 to make 30 or more starts in his first season, was charged with two runs on six hits and two walks over 5 1/3 innings ... Ramirez struck out six and did not issue a walk ... Seattle's Michael Saunders was ejected after striking out to end the 10th ... Jake Arrieta threw 3 1/3 hitless innings in relief for Baltimore ... McLouth finished with three of Baltimore's 10 hits and has seven multi-hit games in September ... Jesus Montero went 0-for-8 for the Mariners.
09/19 07:46:29 ET
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