Djokovic gained revenge for his Olympic loss to Del Potro when he downed the Argentine in straight sets under the floodlights of Arthur Ashe Stadium on Thursday night.
"He was too much for me," said the 23-year-old. "I think he's the favourite to win this tournament. I wish him the best."
Del Potro was the last man to win a Grand Slam title outside of the top three when he clinched the US Open in 2009.