Rybakina stretched her clay-court winning streak to 14 on Sunday at the Caja Magica.
No. 13-seeded Danielle Collins dismantled Jaqueline Cristian in the decider 3-6, 6-4, 6-1 to reach the Mutua Madrid Open round of 16.
Alcaraz has now won 23 on the trot on Spanish clay.
Last week's Stuttgart champ powered into the round of 16 at Madrid.
A fired-up Rafael Nadal out-dueled No. 11 Alex de Minaur 7-6(6), 6-3 to score his first Top 20 win since 2022 at the Mutua Madrid Open.
The top-seeded Pole will face Spain's Sara Sorribes Tormo next.
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