World number 111 James Ward comes back from two sets down to beat American John Isner 15-13 in the final set and put Great Britain 2-0 up in their Davis Cup match.
Isner looked set to level the tie but Ward fought back for a 6-7 (5-7) 5-7 6-3 7-6 (7-3) 15-13 win in Glasgow.
Earlier, Andy Murray beat Donald Young 6-1 6-1 4-6 6-2 to help Britain to a strong position in their world group match.
Coverage of every match is available live on BBC TV, BBC Radio 5 live sports extra, Red Button, the BBC Sport website, mobile, the BBC Sport app and Connected TV.
Saturday, 7 March: Britain v USA, 13:00-16:30 BBC One; 13:00-16:55, BBC Radio 5 live sports extra