Top seeds in a hurry on day of U.S. Open upsets

Novak Djokovic of Serbia chases down a return against Joao Souza of Brazil during their match at the U.S. Open Championships tennis tournament in New York, August 31, 2015. REUTERS/Adrees Latif

NEW YORK (Reuters) - World number ones Serena Williams and Novak Djokovic launched their U.S. Open title bids in ruthless style on Monday, while Kei Nishikori's hopes of making another magical run to the final came to a shuddering halt.

Opening day at Flushing Meadows produced plenty of shock and awe as Djokovic delivered a jaw-dropping performance, speeding past Joao Souza of Brazil 6-1 6-1 6-1 as if the Serb had a taxi metre running outside the National Tennis Center.