Horschel and Bramlett set the pace at Honda Classic
The event at Palm Beach Gardens traditionally marks the start of the Florida Swing but has lost SOME appeal to many of the top players on the tour due to the changes in the schedule.
None of the world's top 10 golfers are playing this week and sponsors Honda are ending their 42 year backing for the event after this year.
Horschel has lamented the decline of the tournament, but the Floridian, who has seven career PGA Tour wins, is hoping to take advantage of the absence of the top stars to finally clinch a win in his home state.
The 36-year-old has been struggling with a sinus infection and said that ailment had counter-intuitively helped him relax for the round, which featured six birdies and a bogey.
"There's a saying - beware of the injured or sick golfer. I'm not like super, super sick, but I'm just not like a hundred percent," he said. "I think you are just sort of, a little bit easier on yourself. You're sort of not worrying about everything."
Starting on the back nine, Horschel sank 30-foot birdie putts on the par-four 11th and 13th holes but then missed a seven-footer on the par-three 15th to bogey.
He got up and down from the bunker for birdie on the par-five 18th and then after the turn enjoyed a streak of three straight birdies from the third hole on.
"The course is really receptive. It's not nearly as firm and as fast as it has been in the past," said Horschel.
"I think that's sort of a conscious thing they have done. The rough's down a little bit. So, the course itself is a little bit softer and it's lending itself to some better scores.
"But you've still got to hit quality golf shots around here. It's not like it's just easy now. You still got to step up and make some good swings on a lot of these holes," he said.
Bramlett, searching for a first win on the PGA Tour, was bogey free, starting his round with a 28-foot birdie putt on the par-four 10th before a brilliant 42-footer for birdie on the par-three 5th hole.
The 34-year-old Californian ended with a birdie on the par-four 9th after a fine approach shot from 119 yards landed 14 feet from the hole.
"I thought my speed on the greens was the biggest thing I took away from today," said Bramlett.
"I felt like I had really good feel for speed all day. I kept it out of trouble off the tee. So when I do those two things I usually score pretty well," he said.
Americans Pierceson Coody and Justin Suh were both in the clubhouse a stroke behind the leaders while Carson Young was one back through 15 holes when darkness stopped play.
Poland's Adrian Meronk, South Korea's Im Sung-jae and English pair Matt Wallace and Ben Taylor were among eight players two shots off the lead.
On a tightly packed leaderboard, 13 players shot 68, leaving themselves just three strokes behind Horschel and Bramlett.