ATLANTA, September 12, 2014 (AFP) - Horschel entered the day tied atop the leaderboard with FedEx Cup points leader Chris Kirk and is now eight-under 132 after 36 holes.
"I drove it actually really good compared to yesterday," said Horschel, who is number two on the playoff points list. "Got off to a hot start and then gave a couple shots away easily.
"My short game was a little dicey. I was able to hang in there and make some good swings on the back side and shoot another four-under par round."
Any of the current top five players on the points list would capture the FedEx Cup title with a win this week. There are others outside the top five who will need a win and some help.
The 27-year-old Horschel finished tied for second two weeks ago at the Deutsche Bank Championship, which was won by Kirk. Horschel is the hottest player on the Tour right now as Friday's 66 was the 10th straight round he has shot in the 60s.
Horschel could do no wrong on the back nine.
"That's the way it's been the last couple weeks," Horschel said.
"I've been playing one side better than the other and I actually probably should have shot a lot lower on the front side today. I had chances.
"I was two-under after three and threw a couple shots away easy, but hey I'll take those two nines again for two more days and see where it puts me."
Kirk carded a two-under 68 on Friday and is tied for second at six-under 134. World number one Rory McIlroy, this year's Open champion and PGA Championship winner, shot a five-under 65 to join Kirk and Aussie Jason Day (67) in second place. McIlroy is number four on the FedEx list.
McIlroy played well on the back nine. He made birdie on 17 and 18 to finish two shots back.
"Great warm-up on the range and from the first tee shot I felt a lot more comfortable out there," McIlroy said.
"I was comfortable with my swing. Comfortable with the shape I was hitting the ball. I still hit a few missed shots out there, but nowhere as many as I did (Thursday)."
Kevin Na (66), Ryan Palmer (67), Cameron Tringale (68) and Jim Furyk (69) are all tied for fifth heading into the third round at four-under 136. Rickie Fowler (68) is in sole possession of ninth at three under.
Masters champion Bubba Watson, currently number three on the points list, stumbled to a three-over 73 and he is eight shots back at even-par 140. Watson began the day one shot back of Horschel and Kirk.
The Barclays winner Hunter Mahan is fifth in points, but he shot a two-over 72 on Friday and is at six-over 146.
Leading scores after Friday's second round of the Tour Championship (par 70, USA unless noted):
132 - Billy Horschel 66-66
134 - Jason Day (AUS) 67-67, Rory McIlroy (NIR) 69-65, Chris Kirk 66-68
136 - Jim Furyk 67-69, Kevin Na 70-66, Ryan Palmer 69-67, Cameron Tringale 68-68
137 - Rickie Fowler 69-68
138 - Justin Rose (GBR) 72-66, Russell Henley 70-68
139 - Matt Kuchar 68-71, Bill Haas 68-71
140 - Sergio Garcia (ESP) 69-71, Bubba Watson 67-73
141 - Adam Scott (AUS) 69-72, Jordan Spieth 71-70, Patrick Reed 67-74
142 - Jimmy Walker 73-69, Zach Johnson 68-74, Martin Kaymer (GER) 73-69, Hideki Matsuyama (JPN) 71-71
143 - Morgan Hoffmann 70-73
145 - Brendon Todd 70-75
146 - Hunter Mahan 74-72, Webb Simpson 74-72, Gary Woodland 71-75
147 - John Senden (AUS) 72-75
154 - Geoff Ogilvy (AUS) 77-77