Neumann completed 36 holes at 5-under-par 139. Defending champion Lorena Ochoa and Hee-Won Han are both at 5 under par through 11 holes of their second rounds.
Rain delayed action on the Iron Horse Course at the Vanderbilt Legends Club and the second round was ultimately called due to darkness. Players will return to the course at 8:30 a.m. ET to complete the second round.
Neumann tallied a birdie at the par-5 fourth and hit her second shot short of the green at the par-5 seventh. She then chipped in for an eagle with a 7-iron and played her approach inside 30 feet at the par-4 13th.
She drained the birdie putt to move to 4 under and knocked her third shot to 15 feet for a birdie at the par-5 14th. Neumann stumbled to a bogey at the following hole but hit her tee shot to 5 feet at the par-3 16th and ran home the birdie putt to get back to 5 under.
'It was kind of a long day, but when you're playing good, it doesn't bother me too much,' said Neumann, a 13-time winner on the LPGA Tour. 'So I'm rolling the ball good, putting well. And after a long day, I'm extremely happy.'
Ochoa picked up three birdies over her first nine holes and moved to 5 under with a birdie at the 10th. She then parred the 11th before the round was suspended. Han had a rocky front nine with five birdies and two bogeys and joined Ochoa at 5 under with a birdie at the 10th.
Heather Bowie fired a 66 to join Stacy Prammanasudh in the clubhouse at 4-under-par 140.
'I just tried to stay patient and know we were going to experience a few delays,' said Prammanasudh, who carded a 70 on Friday. 'But I'm happy with the way I played.'
Wendy Ward stands at 4 under par through 12 holes of her second round.
Jeong Jang and Christina Kim have finished 36 holes and stand at 3-under-par 141.