Tour Championship: Rory McIlroy & Paul Casey chase leader Dustin Johnson

McIlroy won the Irish Open in May and the Deutsche Bank Championship earlier this month

Rory McIlroy and Paul Casey are both five shots off the lead at the Tour Championship as Dustin Johnson remains on course to win the FedEx Cup title.

Johnson shot a three-under-par 67 to lead fellow American Kevin Chappell by one on seven under after round two.

Victory will secure Johnson a $10m bonus, while the fate of England's Casey, who like McIlroy shot 70 to stay two under, is also in his own hands.

World number one Jason Day withdrew from the event with a back injury.

The Australian, who would also have won the overall title with a win at East Lake, pulled out of the BMW Championship eight holes into his final round two weeks ago and lasted just eight holes into his second round in Atlanta.

The top five players in the play-off standings coming into the 30-man season finale - Johnson, Day, Patrick Reed, Adam Scott and Casey - all knew they would claim the bonus with victory.

Casey kept in the hunt with a birdie on the last. He had dropped a shot on the the par-four 17th after failing to get up and down from a greenside bunker.

Scott carded a one-over 71 to drop to level par, while Reed shot 70 to stay three over.

Chappell, who is chasing a first PGA Tour title, needs to win the tournament and for Johnson to finish outside of the top 10 to claim the bonus.

Northern Ireland's McIlroy is in a similar position of needing players in the top five to fade but he remained buoyant at halfway.

He was three over par for his round after eight holes but birdied the 10th, 12th and 17th to move into a tie for fifth.

McIlroy said: "I just didn't feel comfortable with my swing and let that feed in to how I played, especially the first few holes. I made some really sloppy swings and poor shots.

"If I can shoot a couple of scores in the mid 60s at the weekend, you never know."

Johnson, who had a share of the lead after round one, moved clear of the field after mixing five birdies with two bogeys in his 67.

"I played really, solid golf and just didn't get a lot out of it," he said. "I had some close looks that I didn't make.

"Still, three under is a great score around here. I'm never going to be upset with that."

Scotland's Russell Knox says he is in for an "interesting weekend" after a four-under-par 66 lifted him to one under, six behind Johnson.

"The round has put me back in there," he added. "This course is very difficult and a couple more of those and you just never know."

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