Madrid - Kyle Edmund beat Feliciano Lopez in straight sets on Saturday to give Britain a 1-0 lead in their Davis Cup semi-final against hosts Spain.
The world number 69 claimed a hard-fought 6-3, 7-6 (7/3) win over veteran Lopez, who stepped in as a last-minute replacement for Pablo Carreno Busta.
The winners will face Canada in Sunday's final after the North Americans edged out Russia in the first last-four tie.
The 38-year-old Lopez was broken in just the second game of the match as Edmund took the opening set, before seeing two set points come and go in the second.
Edmund clinched his third straight singles victory of the week on his third match point.
Spain need world number one Rafael Nadal to get past Dan Evans in the second singles clash to set up a deciding doubles rubber between Jamie Murray and Neal Skupski and Marcel Granollers and Lopez.