McNeill, at 13-under 203, is trying to win for the first time since the Frys.com Open in 2007, when he was a PGA Tour rookie.
Stenson had 65, while Stadler shot 66.
Australian Matt Jones shot 72 and is in fourth.
Ryo Ishikawa, in Puerto Rico because he failed to qualify for the World Golf Championship this week at Doral, shot 69 and will go into the final round just three shots out of the lead.
Ishikawa, who received a special invitation to the Masters Tournament earlier in the week, never has finished higher than a tie for fourth on the PGA Tour. He is trying to become the fifth consecutive player in his 20s to win on the PGA Tour.
NATIONWIDE TOUR: In Santiago, Chile, Paul Haley II shot his second consecutive 64 to extend his lead to six shots heading into the final round at the Chile Classic.
For the second day in a row, Haley posted the low round.
A former Georgia Tech star, he is at 21-under 195 at Prince of Wales Country Club.
Brad Elder shot 66 and is in second place at 201. Alex Aragon (66), Paul Claxton (66) and Christopher DeForest (69) are all another shot back in third.
NGA TOUR: In Ocala, Fla., Randall Hutchison shot even-par 72 to take a one-shot lead into the final round of the Golden Hills Ocala Classic.
Hutchison is at 6-under 210 at Golden Hills Golf and Turf Club.
Clayton Rotz (71) is a shot back in second.
Former Augusta State star Major Manning, who was tied for the lead after two rounds, shot 75 and dropped back into a tied for third at 212.