Cameron Norrie beat Rafael Nadal for the first time and Katie Swan saw off Nuria Parrizas-Diaz to put Great Britain 2-0 up over Spain in their United Cup group stage encounter.
The 27-year-old had lost his four previous meetings with Nadal.
"He bet me easily the last few times, so it's a great way to end the year for me," said Norrie.
"I was thinking I'd never won a set before against him and I came out firstly wanting to do that.
"I had to stay super patient. It was a super physical match and I enjoyed it.