"I told him, 'Welcome back,'" Astros' manager A.J. Hinch said. "He throws his first pitch 96 mph and his second pitch at 97 ... I think everybody had a smile on their face. He's a big part of what we do in the bullpen."
Fields appeared in his first Major League contest since Sept. 9. He finished strong last season, throwing nine scoreless innings over his final nine appearances.
He picked up where he left off, extending that streak to 10 scoreless innings in 10 appearances.
"I'm glad we were able to get him an inning with a little breathing room," Hinch said. "It feels like an extra-special addition."
Fields is 2-0, with two saves and a pair of holds during the scoreless streak.
He pitched in five games with Triple-A Fresno in a rehab assignment, going two scoreless innings in his last outing on April 20.
Fields rejoins a bullpen already in good shape. Following 2 1/3 scoreless innings Saturday, Houston relievers have a 2.44 ERA, with 14 walks and 60 strikeouts in 55 1/3 innings.