Shortstop Brad Miller, hitting .194 after 17 games in the No. 2 spot, was dropped to ninth.
"We've been playing with the lineup the last 3-4 days, just trying to get more production," said McClendon, who penciled in Ackley fifth for the first time in Sunday's 3-2 loss to the Marlins. "We'll see how things fall out. Hopefully he'll give us a spark."
Ackley, who has hit .345 over his last eight starts, is one of the few recent Mariners' bright spots offensively. He said the key will be not changing his approach just because he's hitting in a different spot in the order.
"The minute I start worrying about the approach I have to take for different spots in the lineup, that's when I'm only hurting myself," he said. "Whether I'm hitting first, fourth, third, ninth, whatever, I have to take the same approach I've taken the whole time since I've started feeling great at the plate. That's just something I can't get away from."
Ackley hit .304 after the All-Star break last year and carried that over to a strong spring. That is far more important to him now than where he's batting.
"It's just mentally being ready to hit from the first pitch on," he said. "If I start worrying about whether I should take these pitches, I have to work the count, stuff like that, that's not where I'm at my best. I just need to stay with the same approach. The situation will dictate a lot of that stuff, but for me it's being up there ready to hit every pitch."
Miller took the move in stride as well.
"Obviously we have to shake things up a little bit and I get that," Miller said. "Ackley has been swinging great. Get him up there and get something going. But the same thing for me. I'm still trying to do the same stuff."
Greg Johns is a reporter for MLB.com. Follow him on Twitter @GregJohnsMLB as well as his Mariners Musings blog. Brian McTaggart contributed to this report. Teddy Cahill is a reporter for MLB.com. Follow him on Twitter at @tedcahill. This story was not subject to the approval of Major League Baseball or its clubs.