Kerfeld made the big league roster out of spring training in 1986, and had a career year posting an 11-2 record and a 2.59 ERA as the setup man for closer Dave Smith. His unexpected performance that year was a key reason the Astros won the National League Western Division title that season. He led the National League in won-loss percentage and finished fourth in the Rookie of the Year balloting. Kerfeld capped his season by pitching four innings and giving up a run in the NLCS. He took the loss in Game 5 when Gary Carter slapped Kerfeld's twelfth-inning pitch for a single, scoring Wally Backman.