World number one Williams continued her utter domination of Maria Sharapova with a 6-4 6-3 win over the fourth-seeded Russian, while second-ranked Li won a rematch of her Australian Open final, beating Dominika Cibulkova 7-5 2-6 6-3 to maintain her perfect record against the Slovakian.
A six-time Miami champion, the American's victory ran her winning streak against Sharapova to 15 matches, a stunning run that stretches back to 2004.
Li's mastery over Cibulkova may not span as many years but is no less complete, the Chinese veteran sweeping all seven of their meetings over a decade-long span.
Three of those wins have come this year, with Asia's first grand slam singles champion defeating the Slovakian in straight sets at Melbourne Park, in three sets at Indian Wells two weeks ago and now at Miami.
"Good challenge. The last time I played her (Williams) was in the (WTA Tour) Championships so it has been four months and this time we really can see how I have improved," Li told reporters as she looked ahead to the final.
"I am really happy I can play her again. Everyone will be confident if they come to the final. I think for sure it will be a tough match."
The 10th seeded Cibulkova had looked ready to deny tennis fans a marquee final between the best two players in the world when she stormed back to take the second set and opened the third with a break to forge a 3-1 lead.
However, Li kept her composure and swept the next five games to cap an enthralling fightback and her spot in the final.
Sharapova and Williams, who have both achieved a career grand slam and held the number one ranking, were expected to develop into one of the great rivalries in women's tennis.
But it has not quite worked out that way with Williams winning 16 of the 18 meetings between the pair.


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