In a match that was moved from Court 1 to the roof-covered Centre Court because of a series of rain delays, Azarenka was broken for the first time when leading 5-4 in the second set. She broke right back but then wasted a second opportunity to serve it out, before converting her second match point in the tiebreaker when Paszek sent a backhand long.
Azarenka, who won this year's Australian Open, reached the semifinals for the second straight year. She will face Williams, who ousted defending champion Petra Kvitova.
Azarenka will overtake the No. 1 ranking from Maria Sharapova if she reaches the final.
Azarenka defeats Paszek to set up clash against Serena
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