TENNIS NEWS - The Dane, who could have reclaimed the top ranking by winning the tournament, was beaten 6-4 7-5 by the Russian.
Romania's Simona Halep, who moved into the quarter-finals with a 7-5 6-1 victory over China's Wang Qiang, will retain the number one ranking.
Kastatkina, ranked 19th, lost 10 of the first 11 points of the match but hit 20 forehand winners on her way to victory.
She overpowered Wozniacki, breaking her serve six times and winning 54% of her first serves.
Kasatkina had previously beaten Wozniacki in straight sets at the St Petersburg Open in February.
She will face Germany's Angelique Kerber in the quarter-finals, following Kerber's 6-1 6-1 win over France's Caroline Garcia.
Kerber, ranked 10th in the world, has won 16 of her 19 WTA matches this season.
Former world number one Karolina Pliskova also made it through to the quarter-finals, beating 16-year-old Amanda Anisimova 6-1 7-6 (6-2).