Serena Williams remains on course for a record sixth win at the Sony Ericsson Open after beating sister Venus 6-4, 3-6, 6-3 to set up a final meeting with 19-year-old Belarusian Victoria Azarenka.
Azarenka defeated Russian Svetlana Kuznetsova 6-3, 2-6, 7-5 in Thursday's other semi-final to book her place in a top tier final for the first time.
In 20 meetings between the Williams sisters, the siblings are now level 10-10 in victories but this match will not go down as one of the better they have shared.
The contest was riddled with unforced errors and lacked the passion of the earlier games on the stadium court in Miami, prompting many spectators to leave before its conclusion.
In the latter stages, Serena managed to hold on to her advantage to close out the match, despite limping with an apparent leg injury.
Azarenka is emerging as one of the bright new faces in women's tennis, having won in Brisbane and Memphis earlier this year and reaching the semi-final at Indian Wells.
The Arizona-based Belarusian wobbled when serving for the match at 5-4, allowing seventh-seed Kuznetsova to break with a double-fault.
But she immediately broke back and got a second chance to serve for the match, this time keeping her cool, despite being pulled back to deuce after a brilliant return from the 23-year-old Kuznetsova.
After the Russian went long at the end of a baseline rally to hand Azarenka the win, she looked emotionally and physically drained.
It had been a tight encounter with both players breaking twice early in the first set but Azarenka getting in front thanks to a superb cross-court forehand into the corner to go 5-3 up.
Kuznetsova dominated the second set but Azarenka passed her test of character as she regrouped.
"All the work I have been doing is paying off. I was just trying to play every point from the beginning to the end," Azarenka told reporters.
"The second set didn't go so well for me, but I was still hanging in there and just played every point no matter what."
Azarenka faced Serena Williams in the Australian Open in January and won a set but then had to retire due to nausea.