The Seattle Mariners have baseball's longest postseason drought, and with a wild-card spot within reach, the club has added a big bat for the stretch run.

Sunday afternoon the Mariners acquired All-Star first baseman Yonder Alonso from the Athletics for outfield prospect Boog Powell. Both teams have announced the trade.

Ken Rosenthal of Fox Sports reports the Mariners claimed Alonso on trade waivers, then worked out a deal. Here's how trade waivers work. The short version: players claimed on trade waivers can only be traded to the claiming team while players who go unclaimed can be traded anywhere.

Alonso, 30, will be a free agent after the season, so he is a rental for the Mariners. They figure to platoon him with Danny Valencia at first base. The left-handed hitting Alonso is hitting .266/.369/.527 with a career high 22 home runs this season, including .286/.391/.557 with 18 of those 22 home runs against righties. Valencia, a righty batter, is hitting .297/.368/.505 with four homers against lefties.

The Mariners have added Yonder Alonso for the stretch run. USATSI

The 24-year-old Powell returns to the team that initially drafted him. He was Oakland's 20th round pick in 2012, then was traded to the Rays in the big Ben Zobrist/Yunel Escobar deal in January 2015. Tampa Bay then flipped him to the Mariners in the Brad Miller/Logan Morrison trade in November 2015.

Powell, who is not related to former Orioles great Boog Powell, made his MLB debut earlier this season and is hitting .194/.310/.194 in 23 games. He put up a .340/.416/.490 batting line with six home runs in Triple-A before being called up. The A's figure to plug him right into their lineup down the stretch.

The Mariners come into Sunday just 1 1/2 games back of the Royals for the second wild card spot. Seattle has not been to the postseason since way back in 2001, Ichiro's rookie season.