James Ward staged a thrilling fightback from two sets down to beat John Isner 6-7 (4/7), 5-7, 6-3, 7-6 (7/3), 15-13 and put Great Britain 2-0 up in their Davis Cup World Group tie against the United States on Friday.
After Andy Murray had earlier seen off Donald Young 6-1, 6-1, 4-6, 6-2 in front of his adoring home crowd in Glasgow, Ward looked destined for defeat as he lost the first two sets against the big-serving Isner.
Isner, the man who triumphed in the longest tennis match in history at Wimbledon in 2010, saved five match points in an epic final set, but Ward eventually prevailed after the world number 20 hit a backhand into the net.
Ward's victory means Britain need one more win from either the doubles on Saturday or Sunday's two singles matches to guarantee success in the first round tie.
Ward and Isner were evenly matched throughout and the Briton had been 4-2 up in the first-set tie-break, but his opponent got a stroke of fortune with a net shot and never looked back.
The American edged further ahead after finally breaking in the 11th game of the second set when Ward was wide with a backhand, finishing the set off with a trademark power serve.
The third set started in a similar fashion with serves being held but Ward brought the house down with two cross-court shots to break in the sixth game, before going on to seal the set with an ace.
The pair remained neck and neck throughout the fourth set but Ward, who is ranked 111 in the world, quickly took control of the tie-break and won 7-3.
American number one Isner prevailed 70-68 final-set triumph against Nicolas Mahut at Wimbledon in 2010, a match that lasted 11 hours and five minutes, and he looked like hanging on in Glasgow but Ward showed no sign of wilting and eventually prevailed to the delight of a vocal home crowd.
- Pretty special -
Earlier, former Wimbledon champion Murray was always in control against Young as the world number five took the game by the scruff of the neck early on and gave few signs of faltering.
"It was pretty special to play in front of a packed arena here," he said of the reception he got in Glasgow.
"I was born here and it's very special. I'm glad I managed to play a good match and get the win."
Two missed overhead smashes from Young handed Murray an early 2-0 lead and the Scot used that to assert his dominance, taking the first set 6-1 in just 21 minutes.
It was more of the same in the second as some outstanding returns from Murray kept Young under severe pressure.
The Scot went two sets up in 46 minutes and a shell-shocked Young was left looking for answers to stem the onslaught.
The American finally won back-to-back serves at the start of the third set and stayed level with Murray to 4-4 with the home player's form dipping.
Young then held serve to lead 5-4 and silenced the Scottish crowd by taking the third set on the back of a rash of unforced errors from Murray.
But it was back to business as usual for Murray early in the fourth set as he again upped his level to grab a vital break of serve in the third game.
He then finished the job off on the back of a second break of serve.
Source: AFP