Results posted early Saturday show Democrat Ron Barber behind Martha McSally by 36 votes out of more than 250,000 cast in the 2nd Congressional District race.
McSally has held a slim lead on all but one day since Tuesday's election as thousands of votes continue to be counted. Barber is seeking a full term after winning a June election to replace his former boss representing the area.
Democrat Kyrsten Sinema has seen her lead over Republican Vernon Parker for the 9th District seat widen to about 4,000 votes.
Both races remain too close to call.