Fiers has thrown 96 pitches Friday night. He allowed a walk in each of the first three innings, but he hasn't allowed a runner past first. The right-hander retired 15 of the last 16, including the last 12.
Fiers has walked three and struck out four.
Josh Turner came close to breaking it up in the sixth inning, but his towering shot to left with two outs hooked foul.
Fiers, who was acquired by the Astros July 30 along with Carlos Gomez in a trade with Milwaukee, is making his third start with the Astros and is still looking for his first win with Houston.
Houston leads 2-0 on Jake Marisnick's two-run home run in the second.