The No. 2-ranked Sharapova conceded only five games in her first four matches, a record at the season's first major.
"Well I'm certainly happy to be playing this well but ... it only gets tougher from here," said Sharapova, who is playing her first tournament of 2013 after pulling out of an exhibition match in South Korea and a warmup event at Brisbane due to an injured right collarbone.
The reigning French Open champion is showing no signs of trouble with the collarbone in Melbourne.
Sharapova has been even more dominant. She started with a pair of 6-0, 6-0 wins -- the first time that has happened at a major since 1985 -- and then beat seven-time Grand Slam winner Venus Williams 6-1, 6-3 in the third round.
"I really want to play against Maria because I lost here last year," Makarova said. "Now I'm pretty confident and I like my game.
"Last year I was so surprised ... and I had so many thoughts in my mind. This year I'm a little bit used to it, so I think I'll be ready to play a good game."
No. 19-seeded Makarova took out the highest seed to lose so far at the season's first major, causing another fourth-round surprise like she did here last year with an upset win over Serena Williams.
Kerber and Makarova were two of only four women in 2012 to beat Williams, who lost only one match in the second half of last season as she collected titles at Wimbledon, the London Olympics, the U.S. Open and the WTA Championships.
"Seems like it was the same this year and last year. Unbelievable feeling," Makarova said. "I really like to play here. The crowd is so perfect."
Nishikori had won two of his previous three matches with Ferrer and was a quarterfinalist in Australia last year, but struggled with 65 unforced errors in the 2-hour, 10-minute match.
Almagro advanced later Sunday, leading 6-2, 5-1 when No. 8 Janko Tipsaveric retired from their fourth-round match.
It will be the first all-Spanish quarterfinal at the Australian Open since 2011, when Ferrer ended Rafael Nadal's bid for a sequence of four consecutive major titles.