This is the reason Nishikori lost in US Open semis

Nishikori cites Djokovic's 'aggressive' play in US Open exit

Kei Nishikori was run ragged by Novak Djokovic in their US Open semi-final on Friday and conceded he had been overwhelmed by the Serb's aggression and energy.

Djokovic needed just two hours and 23 minutes to record a 6-3, 6-4, 6-2 victory at Flushing Meadows as Nishikori came off second best in every department.

"He was playing aggressive. Yeah, I didn't have (much) energy to stay with him. He was hitting side to side," Nishikori told reporters. "Wasn't easy to stay with him tonight."

Nishikori, beloved in his home country and among the world's highest paid tennis players thanks to a bevy of endorsement deals, entered the match with the odds stacked against him, trailing his Serbian competitor 2-14 in their previous meetings.

Djokovic, who won Wimbledon in July, forced his opponent into 36 errors and kept him on the run throughout the match.

"I think I was just tired from last couple matches. I was (trying) to give 100 per cent, but he was playing very solid," Nishikori said. "Maybe if he wasn't Novak, I might have (a) chance to play little better."

"He's playing better everything. He's staying more solid and not giving me many free points," said Nishikori, who reached the final at Flushing Meadows in 2014.