Radwanska took a 13-match winning streak, during which she had won two tournaments and hadn't lost a set, into the match against Li and led 5-4 in the first set. But Li broke Radwanska at love, rallied from a 0-30 deficit to hold for a 5-6 lead and finished off her fourth break to win the set.
Radwanska won the first two games of the second set but Li claimed the next five and survived two break points in taking the ninth game to hold for the match.
Li ended up with six breaks and won 57 percent of the points when Radwanska served.
Sharapova again made short work of her opponent. She's dropped just nine games in her five matches in Melbourne. Makarova notched a break to even the first set at 2-2 but Sharapova won the next six games to take the set and go up 2-0 in the second. She strung together another three-game winning streak and capped the match with her fifth ace of the day.
Sharapova won 70 percent of the points on serve and had 22 winners against 19 unforced errors.
Sharapova owns an 8-4 series edge over Li, including wins in all three of their 2012 meetings.
The other women's semifinal pairing is to be decided Wednesday when world No. 1 and defending Australian Open champion Victoria Azarenka plays unseeded Svetlana Kuznetsova and third-seeded Serena Williams meets No. 29 Sloane Stephens.