TOUR Championship 2016: Friday Leaderboard Scores and Highlights

Dustin Johnson leads the 2016 Tour Championship heading into the weekend after firing a three-under 67 during Friday's second round to leave him at seven under overall. Kevin Chappell is one stroke back and the only player within three shots of the lead.

Jason Day was the day's other headline story. The PGA Tour noted the top-ranked golfer in the world withdrew from the season finale due to a back injury. It's an unfortunate setback for the Australia native, who was in contention at three under through seven holes before being forced to call it quits.

His exit leaves 29 players in the tournament field. Here's a look at the leaderboard following Round 2 at East Lake Golf Club in Atlanta:

It's the second straight event Day removed himself from due to back problems. He did the same during the final round of the BMW Championship two weeks ago with the hope of getting back to full strength for the Tour Championship.

Helen Ross of the PGA Tour's official website passed along comments earlier in the week from the No. 4 seed in the FedEx Cup standings, who stated he felt better and hoped to avoid a setback.

"I'm just trying to ease my way back into it, but the back isn't an issue right now," Day said. "It just happens. It's like you've got to do the small exercises. It's like brushing your teeth every morning. It's that I like them. I just have to do them because it's part of my daily routine now."

Jason Sobel of ESPN provided further details about the withdrawal from Day's management team:

His decision to exercise caution changed the dynamic of the entire event because he looked like a legitimate contender in the early going.

Meanwhile, Johnson maintained his place atop the leaderboard, but he may come back to rue his missed opportunities late in Round 2. He walked to the 17th tee with a two-shot lead before posting a bogey and then failing to take advantage of the par-five 18th.

The silver lining is that he hasn't played his best golf and still finds himself in the driver's seat. He's utilized a mostly conservative approach so far—his driving distance of 291.8 yards is actually below the tournament average—and could ramp things up if needed over the next two days.

Then again, with approach shots like the one highlighted by the PGA Tour on No. 5, taking a little bit off and finding the fairway could be the way to go:

Chappell posted three consecutive birdies starting on the sixth hole to charge up the leaderboard. His hot streak got thwarted by a freak accident on the 11th tee, however—he got stung by a bee.

Randall Mell of Golf Channel provided a look at the second-place golfer getting treatment:

Chappell bogeyed that hole and didn't post a birdie during the rest of the round. While it doesn't seem like an issue that should carry lingering effects into the weekend, he didn't play nearly as well after the incident, so it's something to monitor heading into Saturday.

Looking ahead, even though the event currently has the feel of a two-horse race, East Lake is playing tough enough to keep that second wave of contenders in the mix. A couple mistakes each from Johnson and Chappell would make it a wide-open battle once again.

Rory McIlroy is a player to watch, as usual. He's already completed one massive comeback in the playoffs, making up a six-stroke deficit in the final round to win the Deutsche Bank Championship, and his three-under back nine Friday suggests he could be primed for a similar charge this weekend.

All round statistics courtesy of the PGA Tour's official site.