The move bolsters a Houston bullpen that has struggled at times and has an ERA above 4.00 this season.
Graveman is 4-0 with a 0.82 ERA and 10 saves in 30 appearances this year. He missed nearly a month due to COVID-19 protocols in May and June but has been dominant on the mound. Graveman has not allowed an earned run in his past 12 appearances.
Montero was designated for assignment by the Mariners last week after being acquired in the offseason from Texas.
On Seattle’s side, it’s appears a baffling decision to give up its most dominant reliever while failing to fill a position of need with the Mariners just one game behind Oakland in the AL wild-card race.