Fathauer has already earned a PGA Tour card with a top-25 finish on the Web.com Tour's regular-season money list. The 28-year-old former Louisville player had a 12-under 198 total on TPC Sawgrass' Dye's Valley Course.
A victory Sunday would give him the top priority ranking in the Web.com Tour Finals.
"It would be huge," Fathauer said. "I'm not trying to get that far ahead. It would be a fun day tomorrow if that's what happened. ... Staying patient is huge. Hopefully, I can do that tomorrow."
Blair, needing to earn about $40,000 for a PGA Tour card, shot a 71 in the rain-delayed round.
"Every week you tee it up you want to win," said Blair, a 24-year-old former BYU player. "I'm going to go out, play my game and see where I am at the end of the day."
Jason Gore was third at 10 under after a 66. He also earned a PGA Tour card in the regular season.
Canada's Adam Hadwin, in position to top the Web.com Tour and four-event Web.com Tour Finals money lists, was 8 under along with Jim Herman and Tyrone Van Aswegen. Herman had a 65, and Hadwin and Van Aswegen shot 67.
The Web.com Tour Finals is limited to the top 75 players from the Web.com Tour money list and Nos. 126-200 in the PGA Tour's FedEx Cup standings. The top 25 on the Web.com money list have earned PGA Tour cards. They are competing against each other for PGA Tour priority, with regular-season earnings counting in their totals. The other players are fighting for another 25 cards based on their earnings in the series.
Hadwin leads the four-event money list and is second on the combined Web.com list, $15,736 behind Carlos Ortiz. Ortiz missed the cut. Hadwin won the second Finals event in Davidson, North Carolina.
Fathauer has earned $70,133 in the first three Finals events. With a victory, his total would reach $250,133. Hadwin would need a solo fourth-place finish -- worth $48,000 -- or better to top Fathauer.
Fathauer rebounded from a double bogey on 15 with a birdie on 16 and closed with two pars.
"It was nice to bounce back with a birdie," Fathauer said. "I want to stick to my game plan. I really want to do this for myself."