As big a deal as finally winning an Olympic gold medal was to Novak Djokovic, as much as he has accomplished in tennis — the men's-record 24 Grand Slam trophies, the 99 total titles, the most weeks at No. 1 for any player and on and on — do not for a moment think he is satisfied as the U.S. Open begins. If it seems like there is always some sort of milestone in the offing when Djokovic takes the court, that's because there usually is. This time around at Flushing Meadows, where play begins Monday and the No. 2-seeded Djokovic faces 138th-ranked Radu Albot of Moldova at night in Arthur Ashe Stadium, there is the latest opportunity to get major singles championship No. 25, a total no man or woman ever has reached in tennis.