Nelson, the defending champion, and Gilder, the 18-hole leader, are tied at 10-under-par 134. Jim Holtgrieve (67), Jim Ahern (67) and Walter Hall (69) are all three shots off the lead at 7-under.
Gilder started the day with a two-shot advantage over Nelson and extended it to six through seven holes.
However, Gilder dropped a shot at the par-3 8th, while Nelson birdied the 8th and 9th holes to move to within three shots at 6-under-par.
At the par-5 13th, Nelson cut the deficit to just one when he birdied the hole and Gilder carded a bogey-6.
Both men birdied the par-3 16th. But Nelson pulled even at 10-under when he rolled in a 20-foot eagle putt at the par-5 17th to top Gilders birdie.
Gilder is in search of his second win of the season. Nelson is vying for win No. 4.
Full-field scores from the Farmers Charity Classic