Sharapova had only dropped one set in six career meetings against Makarova, who came into Thursday's match in career-best form, having reached the semis at each of the last two majors.
When Sharapova - who won her sole Australian Open title in 2008 - had to fend off two break points in a long opening game on Thursday it looked as though she would be in for a tough battle.
But the 10th-seeded Makarova dropped her opening service game and despite breaking back in the seventh game, Sharapova was able to steady and win the opening set in 48 minutes.
The second set was largely one-way traffic, with Makarova unable to put the No.2 seed under any consistent amount of pressure.
"It's so special," said the 27-year-old Sharapova.
"It's been a strange road for me to get to the final but I'm here and I'm very happy."
Keys pushed Williams into a tiebreak in the first set and saved two set points with aces, only for the 18-time grand slam champion to prevail at the third attempt.
The second set was not as tight, although Keys saved seven match points in a marathon seventh game which lasted for 11 minutes, forcing Williams to serve the match out.
Williams needed an ace on her ninth match point to finally close out the semi-final after one hour and 24 minutes.
- AAP
