Polona Hercog

What to watch Monday at US Open: Djokovic, Nadal left wrists

All eyes will be on a very important pair of left wrists during Day 1 of the U.S. Open — those belonging to Novak Djokovic and Rafael Nadal.

Defending champion Djokovic, a righty, uses his secondary arm for a two-handed backhand. Nadal, of course, is a lefty who relies on that wing for his heavy topspin forehand that is among the best strokes in the game. How each man looks as he begins a bid for a third career title at Flushing Meadows will be one of the main things to watch Monday at the year's last Grand Slam tournament.

The fourth-seeded Nadal, who beat Djokovic in the 2010 and 2013 finals, plays during the day session in Arthur Ashe Stadium against Denis Istomin...