Sharapova had never lost in five previous meetings against Mattek-Sands and came out firing once again, storming out to a 63 31 lead. Mattek-Sands caught up to 3-all and then 4-all, but served a double fault to drop serve one last time, and the No.3-seeded Sharapova served out a 63 64 win.
When the draw was made, Sharapova definitely had the toughest draw of all the top players - Mattek-Sands had just beaten Agnieszka Radwanska last week. But with a positive ratio of winners to unforced errors, 29 to 28, and negative numbers from her opponent, 18 to 30, Sharapova got it done.
"I knew I had a tough opponent ahead of me," Sharapova said. "Looking at her results in the last couple of weeks and last year and the matches that I've played against her, I knew that it was going to be a tough match. No matter what, I wanted to get through it, and that's what it was about today."
Sharapova was playing her first Grand Slam match since losing in the second round of Wimbledon last June. For one of the all-time Grand Slam greats - she is one of just 10 women to hold the Career Grand Slam - it was a special moment walking back out onto Rod Laver Arena for that return.
"I was happy just to play out there today, despite the heat or anything," the World No.3 commented. "I've been out of the game for a while, so I was just happy to be back in that Grand Slam atmosphere."
Speaking of Radwanska, the No.5-seeded Pole won her opener as well, though it was even more complicated - she was pushed to a third set before finally overcoming Yulia Putintseva, 60 57 62.
Other notable winners were No.2 seed Victoria Azarenka, who made it past Johanna Larsson, 76(2) 62; No.8 seed Jelena Jankovic, who beat Misaki Doi, 61 62; No.10 seed Caroline Wozniacki, who beat Lourdes Domínguez Lino, 60 62; No.11 seed Simona Halep, who routed Polish qualifier Katarzyna Piter, 60 61; and No.13 seed Sloane Stephens, who beat Yaroslava Shvedova, 76(1) 63.
A few lower seeds were picked off on Day 2 as well, with Elina Svitolina beating No.19 seed Svetlana Kuznetsova, 63 63; Marina Erakovic upsetting No.21 seed Sorana Cirstea, 64 76(6); and Garbiñe Muguruza, who just won her first WTA title in Hobart, beating No.24 seed Kaia Kanepi, 62 26 62.
Kuznetsova, a quarterfinalist here last year, was going for the 500th match win of her career.