Seattle is 3-7 this season in one-run games, which leads the American League in losses by a single run.
"We've gone through a lot here the last week," Mariners manager Eric Wedge said after Friday's defeat. "Look at all these tight ballgames, they'll be better for it, stronger for it and wiser for it.
"I keep talking about that hump that we've got to get over. When you get late in ballgames, that's where experience takes over. We're trying to get these young men to the point to where they're comfortable in those situations to where they can execute or produce."