Ridings, the first-round leader, had a 3-under 69 in the second round and shared first with Sterling at 13-under 131.
Bryn Parry had the round of the day at Black Creek Club, a 9-under 63 that vaulted him from a tie for 69th place overnight into a share of third at 11-under 133.
Parry was joined at 133 by Nicholas Thompson (67), Aron Price (65) and Ron Whittaker (67).
There were 16 players within five shots of the leaders, who both entered the weekend looking for their second career Nationwide Tour win.
Sterling claimed his first victory at the Jacob's Creek Open in Australia -- the second event of the season -- which put him at No. 1 on the money list. He has fallen to 18th, but is still safely inside the top 60 for a berth in the Nationwide Tour Championship.
The top 25 players on the money list at the end of the season earn PGA TOUR cards for next season.
'That win seems like a long time ago,' said Sterling, who had seven birdies and two bogeys in the second round. 'I'm pleased because for the last five, six, seven weeks I haven't done a whole lot.'
Ridings has gone considerably longer since his first win, which came at the 2002 Permian Basin Open. He currently sits 86 on the money list, 26 places from making the Tour Championship and 61 from being one of the 25 to get a bump to the PGA TOUR.
'This is satisfying,' Ridings said of being at the top for the first two rounds, 'but there's a long way to go. The weekend is where you make your money.'
Like everyone in the field, the leaders dealt with tough scoring conditions Friday. Ridings was able to string together five consecutive birdies during one stretch.
'The wind was just vicious today,' said Ridings, who made six birdies overall and three bogeys. 'It was swirling all around and was a huge factor. I hit a lot of good shots that didn't end up very well because of the wind.'
For the second day in a row, play was suspended due to darkness. There were three players left on the course when it happened Friday.
The first round was completed in the morning after play was suspended due to darkness on Thursday night.