The pair fell to American third seeds Raquel Kops-Jones and Abigail Spears, 7-5 6-1.
The defeat meant Erakovic and Black missed out on making their fourth final of the year, after finishing runners-up in Madrid, Strasbourg and Birmingham.
Erakovic has a current WTA doubles ranking of 34.
Meanwhile, Kiwi Davis Cup player Michael Venus and his American partner Bradley Klahn lost their semifinal doubles match at the Vancouver challenger event, ending a run of four finals in succession.
They lost to Israeli former world No 5 pair Jonathan Erlich and Andy Ram, 6-3 3-6 10-2.
Venus is at a career-high doubles ATP ranking of 140 and is expected to improve that by around 10 places when the new rankings come out this evening.
In his three challenger events before Vancouver, he won titles at Winnetka and Binghamton and was a finalist at Lexington.
He will partner with American James Cerretani for this week's doubles tournament at the Aptos challenger in California, where they will face Erlich and Ram in the first round.
