The fourth-seeded Radwanska won on her eighth match point to close out a game in which she also saved three break points.
Last year, Radwanska became the first Polish woman since 1939 to reach a Grand Slam final before she fell to Serena Williams. On Thursday in the semifinals, Radwanska will face 23rd-seeded Sabine Lisicki, who knocked Williams out of the tournament then returned less than 24 hours later to beat Kaia Kanepi.
Radwanska had 18 unforced errors to 40 for Li, who won the 2011 French Open.
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