World No.26 Alejandro Davidovich Fokina got Spain off to a flyer on Friday, routing Thiago Seyboth Wild, ranked No.79 in the world, 6-4 6-0.
Brazil levelled the tie, with Haddad Maia grinding down Sara Sorribes Tormo 7-6 (7-1) 6-2.
Haddad Maia was named 2023's Woman of the Year by GQ Brazil after becoming the first female from her country to break into the world's top 10 and reach the French Open semi-finals.
She broke open a tight contest with a flurry of breaks in the second set, ensuring no repeat of a near-four-hour Roland Garros tussle in their last encounter.
The two players were straight back out for the decisive mixed doubles, with Spain going up a set and a break.
However, Haddad Maia had one last push, orchestrating a break with a brilliant return-of-serve winner to get Brazil on level terms in the second set.
They then had two opportunities to level at a set apiece, but Davidovich Fokina saved both points at 4-5, the first thanks to a brilliant albeit slightly fortuitous Sorribes Tormo drop volley after a lengthy rally.Â
Spain then broke the Brazil duo, Sorribes Tormo ripping a backhand through the pair on the decisive point.
She then served it out 6-4 7-5 to take first blood in the 18-country mixed teams event that is in its second year, also hosting teams in Sydney.
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