Andy Murray is an "incredible fighter" after carrying Great Britain into the Davis Cup semi-final with three wins in as many days against France, said captain Leon Smith.
Murray beat Gilles Simon on Sunday - following wins over Jo-Wilfried Tsonga and in the doubles with brother Jamie - to secure the tie 3-1 for Britain.
"He is an unbelievable fighter," said Smith.
"He has a never-say-die attitude. He is so mentally strong."
Murray was a set and a break down against Simon with the effects of the previous two days - a week after a run to the semi-finals of Wimbledon - apparently catching up with him.
But the Scot, 28, revived himself to snatch a second-set tie-break and accelerate away to a 4-6 7-6 (7-5) 6-3 6-0 win over the world number 11.
"It's incredible how he finds a way to dig as deep as he can. It's phenomenal what he finds within himself," Smith added.
"He was a set and a break down, and in the tie break 4-1 down, and he fights, fights and fights.
"He digs into something that he's gone through in his dark places when training.
"He finds a way to do it because his legs and his heart have been conditioned to do it, and he does it better than anyone. I have nothing but immense respect for him."
Great Britain's victory sets up a semi-final, their first since 1981, against Australia.
It comes five years after the team beat Turkey in Smith's first match in charge to avoid dropping into the bottom-tier Group Three Europe of the Davis Cup alongside Andorra, San Marino and Malta.
|Great Britain's Davis Cup record|
|Last final victory: Beat Australia 3-2 in 1936|
|Last final: Lost 4-1 to USA in 1978|
|Last semi-final: Lost 5-0 to Argentina in 1981|
|Champions: 1903, 1904, 1905, 1906, 1912, 1933, 1934, 1935 and 1936|
The only team to match the speed of Britain's recent rise in the Davis Cup's present structure was Croatia, who won the tournament in 2005 after playing in Europe Group Two in 2000.
"When you look at history you see how long it's been since we've been there - that gives you an idea of how difficult it is to do," said Murray.
"We went through a period when we had Tim Henman and Greg Rusedski, who were top-10 players, and never won a World Group match. That shows you how difficult it is to do."