The sixth-seeded Thiem won a spectacular 12-shot rally during his 6-4, 6-0, 6-2 win over Bernard Tomic.
Williams, who is seeded 10th, saved two set points to win 6-4, 7-6 (3).
Makarova will face Lesia Tsurenko or Kateryna Kozlova in round two, with the exit of the top seed adding further intrigue to a draw that was already viewed as wide open with Serena Williams absent.
"Last year was a completely different year", said Kerber after her defeat. But that was about it.
Kerber is not performing to the standards usually associated with the highest ranked player in the game after she won her first two Grand Slam titles at the Australian and US Opens previous year.
The German dropped serve in the next game, with Makarova hitting another four clean forehand winners to consolidate her hold on the match. I mean, of course, it's also a little bit painful the way now.
27-year-old Kvitova defeated American Julia Boserup 6-3, 6-2 in an emotional comeback for her, fans, spectators and several fellow players, who took to social media to congraulate the Czech star. "She's a great champion, so it's a really good win for me". Now I can just enjoy everything - sometimes I just stand outside and see the sun and say, Oh, it s handsome.
The Czech, who spent five months out of the game after needing emergency surgery last December when she was stabbed in her left, playing hand during a burglary, set up a second-round meeting with either Russian Evgeniya Rodina or American Bethanie Mattek-Sands.
"It's a pleasure to be here". "At the end of the match, it was really tough as I knew she wouldn't give it to me - I had to win it", said Makarova, a former semi-finalist at the Australian and US Opens. "Normally I can move very well, but on clay it's always a little bit different and hard for me", she added.
During the match, several members of Kvitova's family wore black T-shirts with white capital letters on the front that read, "Courage".
She pulled back level but was edged out in another tie-break, bouncing her racket in annoyance after serving a double fault on match point.