Unofficial results of Tuesday's election show the 48-year-old dentist unseated North Las Vegas City Councilman Richard Cherchio by one vote; Wagner drew 1,831 votes to Cherchio's 1,830.
Wagner tells the Las Vegas Review-Journal his neighbor's vote put him over the top.
He says he was monitoring election results from home about 10 minutes before the polls closed when he saw the neighbor drive up. Wagner asked the neighbor if he had voted, and the man said no.
So at Wagner's urging, the neighbor high-tailed it to the polls and cast his vote at 6:57 p.m. The polls closed at 7 p.m.
Wagner says winning the seat by a single vote was "unbelievable," and that "every single vote does count."
The 64-year-old Cherchio is promising a recount.