With no players in their quartet ranked in the top 500, Portugal were not expected to put up much resistance and Watson and Konta did their jobs professionally.
Watson got off to a shaky start against Francisca Jorge, 17,but recovered to win 6-4, 6-2 while Konta needed just 49 minutes to defeat Maria Joao Koehler 6-1, 6-0.
The tie came on the same day that the result of Ilie Nastase's appeal was announced following his shocking conduct during last April's World Group II playoff against Romania.
Former world No. 1 Nastase, who was Romania captain for the tie, had his ban reduced but his fine doubled for offences including inappropriate conduct towards GB captain Anne Keothavong and verbal abuse of Keothavong, Johanna Konta and match officials.
Nastase's behaviour somewhat overshadowed Britain's defeat, which condemned the side to another year in the Europe/Africa Zone.
Keothavong's team must top their round-robin group and then win a playoff on Saturday to give themselves another shot of getting into World Group II.