NEW YORK: Always so cool, so consistent, so in control of his emotions and his matches, Roger Federer amazingly let the US Open championship slip from his grasp.

Two points from victory against inexperienced, unheralded Juan Martin del Potro of Argentina, two points from a sixth consecutive title at Flushing Meadows and a record-extending 16th Grand Slam title overall, Federer, quite simply, fell apart on Monday.

He railed at the chair umpire. His legs grew weary. His double-faults mounted. He could not figure out a way to stop the 6' 6" del Potro from pounding forehand after forehand past him. In a result as shocking for who lost as how it happened, the sixth-seeded del Potro came back to win his first Grand Slam title by upsetting the No 1-seeded Federer 3-6, 7-6 (5), 4-6, 7-6 (4), 6-2.