SEATTLE -- With one victory in their previous eight games, the Twins turned to Scott Diamond on Saturday night at Safeco Field, hoping another strong start by the lefthander would help end their slump.
Diamond delivered, but so did Mariners lefthander Jason Vargas.
Each team struggled to push across two runs, and after the Twins missed a big chance in the top of the ninth inning, Seattle won it 3-2 on a sacrifice fly by John Jaso.
Twins manager Ron Gardenhire was saving Glen Perkins for a save situation, so rookie lefthander Tyler Robertson took the mound for the ninth in a tie game.
Michael Saunders singled, and then first baseman Justin Morneau played a sacrifice bunt from Brendan Ryan into a single, failing to get a firm grip on his throw before throwing to a covering Jamey Carroll at first base a shade too late.
Dustin Ackley then failed to get a bunt down on his first two attempts, but ahead in the count 1-2, Robertson lost Ackley to a walk, loading the bases, and Gardenhire turned to rookie righthander Casey Fien.
Jaso entered as a pinch hitter, and on a full count he hit his sacrifice fly to left field.
It was the third time this year the Twins have suffered a walk-off defeat, with the other coming in back-to-back games July 7 and 8 at Texas, in their final two games before the All-Star break.
"You have to have a closer on the road," Gardenhire said. "You can't use [Perkins] for two or three innings because then he's not going to be your closer [Sunday]. We've already used [Jared] Burton, and we have a day game [Sunday].
"You can't throw your closer in the game until you've got a close situation. If we get out of that inning, you'd say the same thing the next inning, over and over, until we put Perkins in there."
Gardenhire noted that Robertson was set up to face a lefthander followed by a righthander and another lefthander, adding, "That's his job to get those guys out."
Robertson (1-1) seemed most frustrated with the walk to Ackley, especially since Ackley went to the plate looking to sacrifice the runners ahead.
"Ackley had a nice at-bat," Robertson said. "I can't walk him there."
In the top of the ninth, the Twins had runners at first and second with two outs and Joe Mauer at the plate. Lefthanded reliever Lucas Luetge fell behind in the count 3-0 before throwing two strikes and then finally walking Mauer to load the bases.
Mauer did not swing at any of the six offerings, even though a base hit could have given the Twins the lead. The Mariners turned to closer Tom Wilhelmsen, and Josh Willingham flied to right field ending the inning.
"We were 2-for-12 with runners in scoring position; that's not going to win you very many games," Gardenhire said.
Diamond gave up two runs on nine hits over 6 2/3 innings, leaving his ERA at 2.95. Vargas also lasted 6 2/3 innings, allowing two runs on eight hits, leaving his ERA at 3.53.
The Twins took a 2-1 lead in the seventh inning on an RBI by Mauer, but in the bottom of the inning, Justin Smoak, who entered the game batting .190, blasting his 14th home run to left-center off Diamond to tie the score at 2-2. The Mariners eventually chased Diamond from the game, but Alex Burnett retired the side without any further damage, leaving the bases loaded. The Mariners left 10 runners on base, but the Twins left 11.