Britain’s Andy Murray went out in the first round of the Bett1 Hulks Indoors event in Cologne, Germany, losing 6-4 6-4 against Spain’s Fernando Verdasco.
Murray, 33, was handed a wildcard to play in the tournament, but was beaten by the 36-year-old world number 62.
Verdasco now faces US Open finalist Alexander Zverev in the second round after the German was given a bye.
Another Briton, Kyle Edmund, lost 7-5 7-6 (7-1) to South Africa’s Lloyd Harris.
Three-time Grand Slam champion Murray, currently ranked 115th in the world, only returned to the ATP Tour in August after career-saving hip surgery.
He beat world number seven Zverev on his way to the third round of the ATP Masters in New York in August, reached the second round of the US Open and then suffered a first-round loss to Stan Wawrinka at the French Open in September.
Against Verdasco, Murray trailed 4-1 in the opening set, pulled a break back in the sixth game but failed to convert two break-point chances in the 10th.
The decisive moment of the second set came in the seventh game when Verdasco broke Murray’s serve.
The Scot saved one match point on his own serve in the ninth game and then had four break points in a lengthy 10th game, before Verdasco, after missing three match points, sealed the victory.
Edmund, 25, ranked 47th, was beaten by the world number 92 for his second successive first-round exit after losing to world number 113 Marco Cecchinato in the opening round of the ATP Masters in Rome last month.
Both Edmund and Harris lost their opening service games, before the South African moved ahead with another break in the fifth game.
Edmund kept the set first alive by breaking back in the 10th game, but Harris immediately broke back again and served for the set, which he took after the Briton failed to take a break point opportunity.
The second set was tighter, but Harris stormed clear in the tie-break to set up a second-round tie against American Steve Johnson.
This event is the first of two indoor competitions in Cologne in two weeks, with Murray again having a wildcard to appear at the Bett1 Hulks Championship.