By The Book

"Be big and show dominance."

—FEB. 23, ON THE EVE OF THE MATCH PLAY CHAMPIONSHIP

On a muggy April afternoon, two days before the Heritage was to begin, Donald stood in a Hilton Head gym and couldn't quite swallow a smirk. "Let's get this over with," he said.

He was being put through his paces by trainers Ben Shear and Craig Knight, part of an ever-expanding team that has spent the last year and a half laboring to eradicate Donald's eponymous disease. Since autumn 2009 Luke has replaced his brother as his caddie, hired the performance coach Alred, welcomed a daughter, tweaked his swing and signed on with Shear and Knight. He first worked with the trainers last November, when they subjected him to a series of diagnostic tests heavy on exotic, golfcentric exercises. Knight's recollection of that first encounter: "Oooh, he flunked that, that, that and that." Donald has been working out six days a week ever since, dutifully quantifying his progress in the black binder. Now it was time to show off for his trainers. Donald snapped off 50 push-ups, whereas five months earlier he had expired at 31. Shear set up a 10-inch step that Donald had to jump atop again and again for 90 seconds. In November he almost passed out after 38 jumps. This time he summited 85 times, his heart racing at up to 170 beats a minute. Donald grunted through more than a dozen other tests of his strength, stamina and flexibility, and his numbers skyrocketed.

Shear looked on like a proud papa. "He's so much more flexible, stable and explosive," he said. "We're not trying to get into a long-driving contest with Dustin Johnson. This is about maximizing Luke's potential."

Donald has become noticeably more muscular, which inspired Jane Park, one of the LPGA's sassier personalities, to recently tweet, "I never realized that Luke Donald had such a ghetto booty." Beyond eliciting electronic catcalls, Donald's fitness has helped his swing, as his trainers consult regularly with Goss to address any of Donald's biomechanical needs. Beginning last winter Luke has successfully ingrained more width in his backswing, less bow in his left wrist at the top and a more proper sequence on the downswing, leading with his legs. "This is the best I've ever swung the club," he says. "I'm longer now. That's due to the gym work and more speed because my swing is more efficient." Donald declines to estimate how many yards he has picked up but says, "I can see it compared to guys I've played with over the years." Donald cut off his woofing with a self-conscious smile. "I'd still like to hit it farther, but I do believe now that what I have is good enough."

This was never more evident than at the Match Play, as he never trailed in six matches while embracing his inner assassin. (From the performance diary that week: "Make everything—no mercy.") Donald concedes that his first U.S. victory in five years "got a pretty big monkey off my back." Just as impressive was his play at the Masters. Donald was three over par through 13 holes of the first round but still got into contention on Sunday despite a double bogey on the 12th hole. "I've always loved watching Luke at the Ryder Cup, because of the way he competes and the way he attacks the course," says Goss, noting his pupil's 8-2-1 record for three victorious European teams. "The Masters was the first stroke-play tournament where I saw that same spirit come out. He fought so hard all week."

The signature moment of the new-and-improved Donald came on the 72nd hole, where his stellar approach shot from an awkward stance hard against a fairway bunker doinked the flagstick and spun off the green. He holed the ensuing chip for his sixth birdie in the final 11 holes and then uncorked the most demonstrative celebration of his career, a double fist pump that he concedes was "really dorky." Says Donald, "I got carried away because it was a little bit of revenge. I said under my breath 'F you' to the flag. It goes back to the philosophy of one shot, one opportunity. In the end I beat the course."

He brought the same intensity to the final round of the Heritage, at which a victory would have propelled him to No. 1 in the world. Donald kept tugging shots left at claustrophobic Harbour Town Golf Links but he stayed in the ball game with a series of improbable par saves, many of them from the sand. ("He's the best bunker player I've ever seen," says Stewart Cink. "I mean anybody.")

Donald was gutted by the loss but that evening, as he cradled his diary, he was already able to see the bigger picture: "Consistently giving myself chance to succeed, getting better in all components." Or, as Tour player Joe Ogilvie put it in a tweet, "Does anyone know where I can get the 'Luke Donald disease'?"