The Mariners recalled Simpson from Triple-A Tacoma on Saturday.
Simpson has coughed up two earned runs in just 2.1 innings with the Mariners this year, but he's turned in a 2.92 ERA and 1.22 WHIP over 12.1 Triple-A frames since making his last big-league appearance May 13. He'll provide Seattle's bullpen with a fresh low-leverage arm, replacing Alex Hoppe.