Andy Murray was unable to reach his first ATP Tour quarter-final since February after Argentina’s Tomas Martin Etcheverry fought back to win a gruelling contest in Basel.
Murray, 36, recovered from a slow start to win the first set in 76 minutes.
But the Briton ended up losing 6-7 (5-7) 6-3 6-2 to the world number 32, who secured victory in over three hours.
Meanwhile, Cameron Norrie lost 6-2 6-4 against fifth seed Alexander Zverev in his second-round match in Vienna.
Former world number one Murray has made a habit this season of being involved in some marathon matches – and the scrap against Etcheverry was another example.
Having stopped Etcheverry going 3-0 ahead, the Scot showed all of his trademark tenacity and endurance to keep his opponent locked in long rallies during a tight opening set which could have swung either way.
Murray trailed in the tie-break before creating a set point with a superb crosscourt forehand winner and converting his chance with a deft volley.
After falling a break down early in the second set, Murray was unable to take three break points as Etcheverry held on in a 16-minute seventh game – which proved key in taking the match to a decider.
Almost two and a half hours were already on the clock and both players needed time to catch their breath before Murray succumbed to a fourth break point in another long opening game.
Murray continued to pressure the 24-year-old Argentine but became increasingly exasperated – often flinging his racquet to the court – as he was unable to create any more chances.
Etcheverry rattled off the final three games and Murray’s fourth loss in five matches capped a disappointing night for the British singles players.
Norrie, who is ranked as the nation’s best player, has struggled for victories in recent months and did not have enough quality to regularly trouble Germany’s Zverev.
The difference in the quality of serving was a key factor, with Norrie landing only 54% of first serves while 2020 US Open runner-up Zverev was powerful and accurate throughout.
A knee injury was another source of concern for Norrie. The left-hander asked for a medical timeout when he trailed 4-3 in the second set and British Davis Cup captain Leon Smith will also be hoping it is not a major problem.
Smith, who has named Norrie in his five-man squad for the quarter-final tie against Serbia in Malaga on 23 November, already faces an anxious wait about the extent of a calf injury suffered by Dan Evans on Tuesday.
Meanwhile, Wimbledon champion Carlos Alcaraz says he will be fit enough to play the Paris Masters and season-ending ATP Finals after a recent foot injury.