Fabio Fognini beat Andy Murray in straight sets to send Great Britain's Davis Cup quarter-final against Italy into a deciding rubber in Naples.
Britain took a 2-1 lead into the final day after Murray completed his singles win over Andreas Seppi on Saturday and then teamed up with Colin Fleming to beat Fognini and Simone Bolelli in a tense doubles clash.
That left Murray knowing a 20th consecutive singles win in Davis Cup would send Leon Smith's team through to a first semi-final since 1981.
But Fognini is one of the best players in the world on clay and his extra nous on the surface came to the fore as he triumphed 6-3 6-3 6-4.
The tie therefore came down to a clash between world number 34 Seppi and Britain's James Ward, ranked 161st and bidding for the biggest win of his life.
Fognini's volatile side had been to the fore over the first two days and he was in full gesticulating mode at the start on Sunday as Murray broke serve in the first game and moved into a 3-1 lead.
But Fognini began to show the huge talent he possesses and he reeled off five straight games to take the first set.
Murray was having to withstand a great deal of pressure, which he managed until 3-3 in the second set.
He had two chances to break Fognini in the sixth game but the world number 13 held on and then broke Murray twice in succession, the Scot ending the set with a double fault.
Murray looked weary, not surprising given the amount of tennis he played on Saturday, while he had been laid low before the tie because of a stomach virus.
The third set was tight as well, but Fognini always seemed to have the upper hand and he struck with Murray serving to stay in the match.
The Wimbledon champion saved two match points, but found the net on the third to send the raucous Naples crowd into raptures.
It was Murray's first singles defeat in Davis Cup since losing to Stanislas Wawrinka in 2005.
Fognini told the BBC: " I just played better than Andy. We know this sport is really difficult and Andy played a lot yesterday. It was an important point for me especially and for Italy. I did my best and I played unbelievably."