Ghent - David Goffin clawed his way back from a two-set deficit to defeat British newcomer Kyle Edmund 3-6, 1-6, 6-2, 6-1, 6-0 and give Belgium a 1-0 lead in the Davis Cup final in Ghent on Friday.
It brought his singles record in the competition to 12-2, his two previous losses both coming in five-setters after he had led by two sets to love. It was the first time in his career that he had won a match after losing the first two sets.
Edmund, meanwhile, came up short in his bid to become the first player to win a live rubber while making his debut in the competition in the final.
But with world number two Andy Murray to follow in the day's second singles against lowly-ranked Ruben Bemelmans, Britain were still well-placed to draw level by the end of day one.
"It was not easy. Kyle had good intentions and was really heavy with every forehand," Goffin said.
"It was hard for me to find my timing. I knew if Kyle was playing like this, bravo, but if there was a small chance I had to take it.
"He played really heavy and I was surprised. He played really aggressive with his forehand."
The British are seeking a 10th Davis Cup title overall, but a first since 1936, while Belgium have never won the competition.
Edmund, ranked 100th in the world, 84 places below Goffin, needed 12 minutes to hold his opening serve, but he then silenced the majority Belgian fans inside the 13 000-capacity Flanders Expo by reeling off the next four games to lead 5-0.
The 20-year-old South African-born player missed a set point in the next game, but after Goffin had battled his way back to 5-3, the British youngster made no mistake on his next serve.
Edmund, who won a second-tier challenger tournament on clay in Argentina earlier this month to grab the attention of British captain Leon Smith, stayed on top in the second set with some thumping forehands.
Goffin held his serve to open, but Edmund then rattled off six games in a row to take the set 6-1.
The situation was getting desperate for Goffin and Belgium, but Edmund's game finally faltered early in the third set and Goffin pounced with breaks in the third and fifth games.
He won the set 6-2 and, with Edmund starting to look leg-weary, he dominated the fourth set from the start to force a decider.
Goffin held serve to open with and when he broke to 15 in the next game, there was no way back for his shattered-looking opponent as the Belgian won 12 games in a row.