British number one Kyle Edmund is through to the second round of the Cincinnati Masters after beating American wildcard Mackenzie McDonald.
Edmund, 23, dropped only one point on his serve and hit 10 aces in the 6-3 6-2 win.
The world number 16 will next play the winner of American Frances Tiafoe or Canada's Denis Shapovalov.
World number one Rafael Nadal withdrew from the tournament after winning the Rogers Cup in Toronto on Sunday.
The US Open, the final Grand Slam of the year, starts on 27 August.
"No other reason than personally taking care of my body and trying to keep as healthy as I feel now," said Nadal.
The withdrawal leaves Roger Federer as the top seed in Cincinnati. The Swiss 20-time Grand Slam winner had missed the Rogers Cup as part of his strategy to prolong his career.
Former world number one Andy Murray opens his Cincinnati campaign against Frenchman Lucas Pouille on Monday from 16:00 BST, while Stan Wawrinka and Novak Djokovic are also in action.