Debutant Jack Draper (21) repaid Britain skipper Leon Smith's faith in him by giving the hosts a superb start, as he came from behind to seal a 6-7, 6-3, 7-6 win over Thanasi Kokkinakis (27) in front of the partisan home crowd at the Manchester Arena.
"There's nothing better, a real battle and a massive crowd here," Draper said. "It's amazing to play my first Davis Cup tie in the UK in this sort of arena. I'm so grateful to be here and I'm happy Leon trusted me and put me out here today.
"I'm playing for my country so I had to put everything on the line... the team's dialled in this year, we want to get to the Finals after a tough run last year."
Britain, bidding to reach the quarter-finals from Group B after missing out for the first time since 2018 last year, then completed the victory when an inspired Dan Evans (33) beat world number 12 Alex de Minaur (24) 6-1 2-6 6-4.
In Valencia, the Czech Republic took an unassailable 2-0 lead over hosts Spain, who were missing Carlos Alcaraz (20) after the world number two decided to pull out of the squad to recover following his US Open semi-final defeat.
Tomas Machac (22) cruised past Bernabe Zapata Miralles (26) 6-4 6-4 and Jiri Lehecka (21) doubled their lead, downing Alejandro Davidovich Fokina (24) 7-6, 7-5 to put them in a strong position in Group C alongside Serbia, who won their tie on Tuesday.
The top two teams from each of the four groups will advance to the knockout rounds in Malaga, which take place in November.
Italy also endured a disappointing day in front of home fans in Bologna, as defending champions Canada secured a comfortable Group A victory in a re-match of last year's semi-final.
World number 200 Alexis Galarneau (24) beat Lorenzo Sonego (28) 7-6, 6-4 and the 158th-ranked Gabriel Diallo (21) stunned Lorenzo Musetti (21) 7-5, 6-4 as Canada showed they can be a force even without Denis Shapovalov (24), Felix Auger-Aliassime (23) and Milos Raonic (32).
Italy are without Jannik Sinner (21) and Matteo Berrettini (27) this week but still have three top-50 singles players in the squad.
In Split, the United States got off to a good start against hosts Croatia as Mackenzie McDonald (28) downed Dino Prizmic (18) 6-4, 6-2 but Borna Gojo (25) levelled the Group D tie by beating world number 11 Frances Tiafoe (25) 6-4 7-6(6).
But the US pair of Austin Krajicek (33) and Rajeev Ram (39) edged out Ivan Dodig (38) and Mate Pavic (30) 7-6, 6-7, 6-2 in the doubles rubber to ensure a 2-1 victory.
