Roger Federer punctuated his latest U.S. Open victory Sunday with a shot he called, quite simply, the greatest of his life: a between-the-legs, back-to-the-net, cross-court winner from the baseline. A point later, with the crowd in hysterics and opponent Novak Djokovic still in shock, the world’s top-ranked player closed out the victory, 7-6 (3), 7-5, 7-5, to move one win from his sixth straight U.S. Open title. OK, who’s got next? Juan Martin del Potro is the lucky guy whose first career Grand Slam final will come Monday against Federer, who made his 17th in the last 18. Earlier, No. 6 Del Potro beat No. 3 Rafael Nadal, 6-2, 6-2, 6-2. It’s the kind of shot every tennis player has tried — oh, a thousand times or so. Federer practises it, too. “A lot, actually,” he said. “But they never work. That’s why, I guess, it was the greatest shot I ever hit in my life.”