Seattle didn't draw any consolation from another close loss.
Tampa Bay's 4-3 win Thursday gave the Rays a four-game sweep of the Mariners, who dropped three one-run decisions and the other by two.
"Tough ballgames, tough losses. We're just not quite doing enough to finish off innings to take that lead back, especially on the road," Mariners manager Eric Wedge said. "There are good things that are happening daily with different individuals, but collectively we're not doing enough to get over that hump."
Jeff Keppinger hit a two-run homer and Desmond Jennings added a two-run triple to back Jeff Niemann (2-3), who allowed three runs and seven hits over 5 2-3 innings as the Rays extended their winning streak to five with their 11th victory in 12 games.
The Mariners concluded a 10-day, 10-game road trip with a season-longest six-game losing streak. The skid came right after a four-game winning streak that included a sweep of Detroit to begin their three-city trip.
The Rays scored all of their runs in the second inning, with Keppinger and Jennings delivering the biggest hits of the day off Kevin Millwood (0-3).
"Some balls found holes, they hit a gap and that was pretty much it," Millwood said. "I felt like I was throwing the ball pretty well. I tried to keep the ball down and mix speeds."
Reliever Jake McGee retired all seven batters he faced, and Fernando Rodney worked a scoreless ninth inning for his ninth save in nine opportunities for Tampa Bay.
The inconsistent Mariners struck out eight times, hiking their total in the series to 46. They have been held to 12 runs during their skid.
Millwood retired the first two batters of the second inning before giving up an infield single to Will Rhymes and Keppinger's second home run of the season. The next two batters, Chris Gimenez and Sean Rodriguez, singled and scored when Jennings tripled to right-center field for a 4-2 lead.
The Mariners got one of the runs back when Dustin Ackley doubled with one out in the fifth and scored on Ichiro Suzuki's double down the right-field line.
But Seattle continued to struggle with runners in scoring position, stranding the potential at second base in the fifth and sixth innings. John Jaso doubled leading off the sixth, but Niemann struck out Mike Carp and Justin Smoak.
Niemann departed after throwing 107 pitches. McGee fanned Michael Saunders to end the threat.
"There's not one thing you can put your finger on," Millwood said of the Mariners' problems in close games. "We just need to play better."
NOTES: Tampa Bay CF B.J. Upton sat out after leaving Wednesday night's game after the fifth inning because in his right quad muscle. The Rays don't think the injury is serious. Jennings shifted from left field to center field and Brandon Allen started in LF. ... The Mariners have lost eight straight games to Tampa Bay. ... Seattle flies home to open a weekend series Minnesota on Friday night. LHP Jason Vargas (3-2) gets the start against RHP Carl Pavano (1-2).