Jaeger, Brehm and Schenk all sit on top at 5. Jordan Spieth, Tommy Fleetwood, Justin Thomas and Sam Burns are within three strokes of the lead and all looking for their first wins of the season.
Brehm was the standout performer with a hole-in-one on the par-3 17th hole for a 5-under 66.
Stephan Jaeger also had a 66, while Adam Schenk sits beside the trio with the low score in the afternoon. Jaeger has the shortest odds of the bunch, and he hit the ball the best on Thursday as he finished third in the field in approach play.
The leading trio will most especially be aware of Spieth breathing down their neck as the 2015 tournament winner showed strong putting skills to end just one back of the leaders.
Spieth, on his return to Innisbrook for the first time in five years, had a bogey-free round and shone with the putter, making birdie putts of 60 feet and 30 feet on his way to a 67. Also at 67 were former U.S. Open champion Lucas Glover and Maverick McNealy.
Jaeger, Brehm and Schenk have had only one top 10 finish between them in 75 attempts and so it would be a major surprise if either won with Spieth emerging as a favourite.
Burns, who has won the tournament a couple of times, looked most accustomed to what is known to be a difficult course with tree-lined fairways, elevation and not nearly as much water.