CARMEL, Ind. — U.S. Open champ Dustin Johnson doesn't care about the physics behind his new putter. Seeing more putts drop is enough for him. Johnson made two eagles in a span of seven holes, shot 31 on the back nine and set the course record at Crooked Stick with 9-under 63 Friday that gave him a share of the lead with Roberto Castro in the BMW Championship. Johnson didn't know he set the course record until Tony Pancake, golf director at Crooked Stick, congratulated him en route to the clubhouse. "I guess no one was ever better than 63," Johnson said with a shrug and a smile. Castro was the first player to reach 14-under 130 on the rain-softened course. He kept bogeys off his card, rolled in a pair of 30-foot putts and had another 65 in his last-minute bid to get to the Tour Championship at East Lake in Atlanta, just 15 minutes from his house. Castro is No. 53 in the FedEx Cup and only the top 30 make it to the FedEx Cup finale at East Lake and a shot at the $10 million bonus. Paul Casey, who had the 54-hole lead last week at the TPC Boston until finishing two shots behind Rory McIlroy, had 66 and was three shots behind. Johnson has had one of the most consistent years with 12 finishes in the top 10, along with wins in the U.S. Open and a World Golf Championship at Firestone. Even so, frustration began to set in when the putts stopped falling, so he switched to the TaylorMade Spider. "I was just struggling to get the ball to come out on the line I was seeing," Johnson said. "No matter what I did, how much I practiced, training aids, whatever. It just wasn't working. So just decided to switch it up." When asked about the physics involved, Johnson said, "I don't go into that stuff — as long as it goes where I'm looking." That said, he did point out he took physics in high school. "I got an A, too, bud." Johnson already was virtually assured of being among the top five going into the Tour Championship, meaning he only has to win at East Lake to win the FedEx Cup. Along with what he described as "10 million reasons" why he wants to win, other rewards are available. He already is regarded a favorite for PGA Tour player of the year, and he is likely to move ahead of Jason Day in the Vardon Trophy race for the lowest scoring average.