Player-caddie split ups are a common occurrence on tour, but recently some of the more high-profile relationships have ended. First, it was Phil Mickelson and Jim “Bones” McKay splitting up after 25 years together. Rory McIlroy and J.P. Fitzgerald’s break up followed soon after. Both have led to mixed results, at best.

It’s impossible to say whether any of these separations have any real affect on a player’s performance, but for Jason Day, it so happens that he matched his second lowest round of the season overnight at the BMW Championship, one day after news broke that he was replacing longtime caddie Colin Swatton on the bag. The Australian posted a seven-under 64 at Conway Farms Golf Club in Chicago and trails countryman Marc Leishman by two shots.

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Day, 29, got off to an inauspicious start, bogeying the par-3 second hole. It would be the only shot he dropped all day, and he got it back with a birdie at the par-4 fourth. Four holes later, he struck a 188-metre approach shot at the par-5 eighth to three feet and holed the eagle putt, then made par at the ninth to turn in two-under 33. He was dialled in with his irons on the home nine, making five birdies, only one of which came outside seven feet. His 1.4 putts per green ranked first in the field in round one.

He’s chasing Leishman, who carded a nine-under 62 that featured 10 birdies and a bogey. The reigning Arnold Palmer Invitational winner is coming off a strong performance at the Dell Technologies Championship, where he finished third after leading with nine holes to play. He’s never missed a cut in seven tries at the BMW Championship.

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Tied with Day at seven-under is Charley Hoffman, who looks to continue a strong season that saw him earn a Presidents Cup captain’s pick. Hoffman is in search of his first victory of the season, and fifth of his career. He’s given himself plenty of chances this season, with four finishes inside the top three.

Also at seven-under is Jamie Lovemark, who striped a 251-metre 3-wood on the 18th hole to seven feet and rolled in the eagle putt. Sitting at 58th in the standings entering the week, he will need a strong result to earn a spot in the Tour Championship. He’s currently projected inside the top-30 (19th) thanks Thursday’s low round.

Jordan Spieth, Keegan Bradley, Rickie Fowler and Rafa Cabrera Bello all shot six-under 65s and are just three off the lead. Four behind is Phil Mickelson, who posted a bogey-free five-under 66, the same score returned by the third and final Australian in the field: Cameron Smith.

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