Graveman, a 30-year-old right-hander, has been dominant this season with an 0.82 ERA in 33 innings pitched. He is 4-0 and has 10 saves this season.
Despite moving Graveman, the Mariners are still looking to add players, sources told ESPN’s Jeff Passan, and could be very active over the next 72 hours.
With Graveman gone, right-hander Paul Sewald, who is 6-2 with four saves and a 2.30 ERA in 31⅓ innings this season, likely will step into the closer’s role.
The Mariners had designated Montero for assignment on Friday. The 30-year-old right-hander is 5-3 with seven saves and a 7.27 ERA in 43⅓ innings this season.
Toro, 24, is hitting .211 with six home runs and 20 RBIs for the Astros this season.
Smith, a 37-year-old right-hander, is 1-1 with a 7.48 ERA in 21⅔ innings this season.
The trade comes a day after the Mariners rallied from a 7-0 deficit to stun the Astros 11-8. The surprising Mariners enter Tuesday’s games just six games behind the Astros in the American League West standings.
The Mariners and Astros continue their series in Seattle on Tuesday night.