Cameron Norrie was the star for Great Britain as they levelled the Davis Cup tie with Spain 1-1 after the first two singles.
A team shorn of Andy Murray and Kyle Edmund outperformed expectations on the first day in Marbella in their World Group clash.
The first match of the day saw Liam Broady beaten in straight sets by Albert Ramos-Vinolas.
I wanted to keep the points physical and work as hard as I could.Cameron Norrie
Then Norrie, the world number 114 faced Roberto Bautista Agut and the home favourite stormed into a two sets to love lead to leave Britain staring at a 2-0 overnight deficit in the best of five tie.
The Spaniard then secured an early break to lead in the third set, but, playing the match of his life, Norrie somehow came back into the contest.
He broke the Bautista Agut serve three times to claim the third set, then went a break up in the fourth with the Spaniard taking a medical time out.
The Brit claimed that fourth set to level the match and, cheered on by 1,000 British supporters in the crowd, he went a double break up in the deciding set to complete the comeback and give Britain a chance of progressing through to the quarter-finals.
The teams play a doubles match on Saturday with Jamie Murray and Dominic Inglot taking on Feliciano Lopez and Pablo Carreno before the concluding two rubbers on Sunday.
Britain are 11/10 to win the doubles with Spain 4/6.
Norrie gave his reaction to the best win of his career so far. On court immediately after the win he said: "I was nervous and had a streak in the second set where I couldn't get a serve but I pulled it together.
"I noticed he was struggling a little bit in the fourth set. I backed myself physically and mentally against the guy and I'm just chuffed to get through it. I wanted to keep the points physical and work as hard as I could."
Meanwhile Kyle Edmund is 80/1 to win this year's Wimbledon with Roger Federer priced at 7/4.
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