Djokovic's right arm troubles him at US Open; Keys wins
Seconds later Monday night, a weak serve produced a wince from the U.S. Open's defending champion, then was followed by a missed forehand that gave away a set — the first set dropped by Djokovic in the first round of any Grand Slam tournament since 2010.
The others were 20th-seeded John Isner's comeback from two sets down to edge 18-year-old Frances Tiafoe before a rowdy, standing-room-only crowd at the new Grandstand, and 26th-seeded Jack Sock's five-set victory over another 18-year-old, Taylor Fritz.
More drama, too: A first-round loss by Rio Olympics gold medalist Monica Puig, and French Open champion Garbine Muguruza's complaints about having trouble breathing after dropping the first set of a match she would go on to win in three.
The wrist appeared to be just fine against Janowicz, a former top-20 player who reached the semifinals at Wimbledon in 2013 and is now ranked 247th after his own series of injuries.
Earlier in Arthur Ashe Stadium, Rafael Nadal stood near the net after winning his first Grand Slam match in three months — 6-1, 6-4, 6-2 against Denis Istomin — and unraveled the thick wrap of white tape protecting his all-important left wrist.
Nadal's afternoon match was played with the new $150 million retractable roof open under a blue sky, while offering some extra shade on a day when the temperature reached 90 degrees.
Both Nadal and his coach, Uncle Toni, described the way Rafael changed the way he hits a forehand during the Rio Games to try to avoid pain.