The team's two most reliable relievers over the season were unable to get the six outs needed for the Mariners to move one game closer to the second-place Rangers, resulting in a 7-4 loss before 27,899 on Fan Appreciation Night at Safeco Field.
Right-hander Mark Lowe surrendered the tying run in the eighth inning and three consecutive singles with two outs in the ninth inning off closer David Aardsma triggered a three-run Rangers rally and a guaranteed second-place finish for the visitors.
The Mariners had to sweep the three-game series to tie Texas in the AL West.
"We've talked about putting ourselves in a position to win, and we did that tonight," manager Don Wakamatsu said. "The bottom line is they scored a lot of runs with two outs."
The Mariners' fourth run of the game also came with two outs, as second baseman Jose Lopez delivered a run-scoring single to right field in the fifth inning. Lopez's 94th RBI of the season scored shortstop Josh Wilson from third base, giving the Mariners a 4-3 lead.
The lead lasted until the eighth.
Lowe, making his career-high 75th appearance -- 18 more than his previous single-season highest workload -- surrendered a leadoff double to Andruw Jones, but nearly escaped the instant trouble.
However, Michael Young drilled a single to right field that scored pinch-runner Estaban German with the tying run. Lefty reliever Jason Vargas came in to get the final out of the inning.
Adrian Beltre doubled with two outs and stole third in the bottom of the eighth inning, but was left stranded on third.
Wakamatsu called on Aardsma to keep the series opener tied. The first two batters were retired, but three consecutive singles produced the go-ahead run, and Elvis Andrus greeted Randy Messenger with a two-run double.
"We had an opportunity late in the ballgame to break the tie and we didn't do it with two outs," Wakamatsu said. "The timing of our hitting was not good, but theirs was."
The Mariners erased a three-run deficit in the fourth inning when Adrian Beltre singled home a run and Mike Carp plated two more with a single into left-center, the second of his three hits in the game.
Right-hander Ian Snell made his final start of the season attempting to make it five consecutive seven-inning-plus outings for the Mariners' rotation.
He got off to a rocky start, threw a lot pitches early and made it through six.
"I thought he pitched a little bit tentative early, a lot different than his last outing in Toronto," Wakamatsu said. "But give him credit. He came back, battled and finished with three scoreless innings."
Snell escaped the first inning unscathed, stranding two runners, but surrendered two runs in the second inning.
A one-out walk to Jones, batting .207, was the second free pass Snell allowed, and became the first one to hurt him. Catcher Taylor Teagarden drilled a ground-rule double to right-center and Jones scored on an infield out.
Julio Borbon followed with a run-scoring single up the middle.
Another walk haunted Snell in the third inning, this time a leadoff pass to David Murphy. After Marlon Byrd singled, both runners advanced on a sacrifice bunt and Murphy scored on Chris Davis' single to left field.
"I didn't have command of anything, but I found a way to get out of trouble and kept the team in position to win the game," Snell said. "The season is done for me, and I will spend the offseason concentrating on going after the hitters, not picking."
Acquired from the Pirates on July 29, Snell posted a 5-2 record for the Mariners.
"I have come a long way from being over there in Pittsburgh," he said. "I have to say thank you to the fans. They supported me ever since I got here. It has been pleasant and I look forward to hopefully being here for the rest of my career."
Carp led Seattle's offense with a career-best three hits and his first multi-RBI game.
The chances for a four-hit game were dashed when he was removed for a pinch-hitter in the eighth inning.
"It would have been nice to have gotten a chance there," he said, "but Sweeney is better suited to be up there in that situation [against left-hander C.J. Wilson]. Unfortunately, it didn't work out."
Sweeney took a called third strike to end the inning.
"We had to be tough tonight and we were," Rangers manager Ron Washington said. "We went out there and did what we had to do to get it done."
The Rangers will wind up in second place this season -- largely because of the way they have played the Mariners -- winning 11 of the 17 games played.
"It means everything," said Washington of finishing second. "If we can't get first, we want to get second."
Jim Street is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.