Williams, 30, vanquished Azarenka 6-3, 7-6 (8-6) in a semifinal match to improve to 8-1 lifetime against the 22-year-old Belarusian and reach her 18th major final.
Serena, a former world No. 1, overpowered Azarenka in the first set with a crushing serve before she managed to break Williams and tie the second set at 3-all. After staying on serve over the next six games, Williams won the tiebreaker with a Wimbledon-record 24th ace.
Poland's Radwanska, 23, blitzed No. 8 seed Angelique Kerber of Germany 6-3, 6-4 in 70 minutes and could become the No. 1 women's player in the world if she beats Williams, who is seeking a fifth Wimbledon title, on Saturday. The winner takes home $1.8 million.
Kerber, 24, was appearing in her first Wimbledon and second career Grand Slam semifinal (0-2).