Kyle Edmund produced a valiant show as Alexander Zverev beat him 7-5, 7-6 (13/11) at the Internazionali BNL d'Italia in Rome.
Edmund went out after an epic second set tie-break in which he saved seven match points.
The British No.1 had two set points in the second set, but he was unable to stop the defending champion reaching the quarter-finals.
Zverev came into the match in excellent clay court form after recent successes in Munich and Madrid.
The German seemed on a comfortable course for his 11th successive win as he took an early advantage.
But Edmund broke back to level at 5-5 before Zverev responded by taking the next two games.
Edmund was soon a break down in the second set, but he won three games in a row to make it 5-4.
He was unable to take a set point as Zverev made sure of a tie-break which will be long remembered.
Edmund saved three match points at 6-3 down and then led 7-6 to stand on the brink of forcing a deciding set.
But Zverev saved a second set point for Edmund and eventually accepted his eighth match point to set up a date on Friday with Belgium's David Goffin.
In the women's singles, it was no birthday victory for Johanna Konta as she lost to French Open champion Jelena Ostapenko in the third round.
Konta, celebrating her 27th birthday, could not build on a fine start and her search for a top-10 victory in 2018 goes on after sixth seed Ostapenko fought back to win 2-6, 6-3, 6-4.
The British No.1 was looking to reach the quarter-finals in Rome for the first time and was hugely impressive in the opening set against a below-par Ostapenko, who complained of feeling dizzy.
But the Latvian showed with her stunning victory at Roland Garros last summer that she possesses some of the most potent attacking shots in the game and she began to find her groove in the second set.
After going 2-0 down, Konta fought bravely to stay in contention in the decider, saving a succession of break points, but she could not break the Ostapenko serve and slipped to defeat after two hours and 13 minutes.
Despite the defeat, it was another encouraging performance from Konta and further signs she is recovering the lost confidence that has seen her ranking slip to 22nd.
Mervyn Davies, meanwhile, has been appointed as the new chairman of the Lawn Tennis Association and will succeed David Gregson at the end of September.
Like Gregson, Lord Davies comes from a business rather than sporting background and also held several ministerial positions in the last Labour government.
He is currently partner and chairman of private equity firm Corsair Capital, chairman of investment business LetterOne, senior independent director at Diageo and chairman of the trustees of the Royal Academy Trust. He was made a peer in 2009.
A keen tennis enthusiast, he has experience within sport as a former member of the board at Tottenham and a current non-executive director of World Rugby.
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