Cameron Norrie beat Dan Evans 7-6 (7-5) 7-6 (8-6) to record his second straight win over the British number one at the Battle of the Brits team competition.
That impressive victory was one of five from eight matches for the British Bulldogs side, who lead the Union Jacks 29-12 after day three.
British women's number two Heather Watson gave the Jacks a good start with a 3-6 6-1 10-6 win over Eden Silva.
However, Jamie Murray lost both his doubles matches for the team.
Murray's first defeat was with partner Katie Boulter as they went down 3-6 6-4 10-8 to Norrie and Beth Grey, who had earlier beaten Naomi Broady 6-3 6-2, in the mixed doubles.