Lewis, 54, captured the semifinal match with a birdie on the first hole of sudden death after Smith had eagled the 18th to draw even. Smith is trying to capture the tournament for the third year in a row and become a four-time winner of the event overall.
Smith is tied with Jay Sigel for most victories all time in the Mid-Amateur, which is open to all non-professionals who are at least 35 years old.
The winner of this tournament each year receives one of the six invitations handed out to amateurs by the Masters. The others are the finalists in the U.S. Amateur and winners of the British Amateur, Asian Amateur and U.S. Public Links Championship.
The other semifinal Wednesday went to Kenny Cook, who overwhelmed John Engler 6-and-5. Thursday's championship match is scheduled for 36 holes at the Shadow Hawk Golf Club.