Andy Murray was beaten by Richard Gasquet in his first singles match since hip resurfacing surgery in the first round of the Cincinnati Masters.
The British former world number one lost 6-4 6-4 to France's Gasquet.
Murray 32, broke down in tears at the Australian Open in January, fearing surgery on his long-standing hip injury may end his chances of playing singles.
Instead surgery has left him pain-free, allowing the three-time Grand Slam champion to resume his career.
The Scot returned to competitive action in the Queen's doubles in June - going on to win the tournament alongside Spain's Feliciano Lopez - and has played in four more doubles events.