The Seattle Mariners, hours after trading their best reliever, are finalizing a deal to acquire left-handed starter Tyler Anderson from the Pittsburgh Pirates, sources told ESPN's Jeff Passan on Tuesday night.

It wasn't immediately clear who the Pirates were getting in return.

Pittsburgh thought it had a deal for Anderson with the Philadelphia Phillies earlier Tuesday, but it fell through on medical review, sources said.

Seattle instead moved to acquire the 31-year-old Anderson, who is 5-8 with a 4.35 ERA this season. He's set to become a free agent after the season.

Anderson spent his first four big league seasons with the Colorado Rockies before joining the San Francisco Giants as a free agent last season and then the Pirates this year. He's gone at least five innings in each of his 18 starts in 2021.

Earlier Tuesday, Seattle traded right-hander Kendall Graveman to the Houston Astros as part of a four-player deal that baffled some considering the Mariners are just one game behind the Oakland Athletics in the AL wild-card race.

But Mariners general manager Jerry Dipoto hinted more moves could be on the way -- which turned out true with the team nearing the Anderson deal.

"It probably doesn't as a standalone, but it's part of a context that's going to be an ongoing story over the next couple of days'' as the trade deadline nears, Dipoto said when asked why the team traded Graveman.

"What comes next could be as early as tonight or tomorrow because we do plan on being active."