Muguruza overcomes Kasatkina, Mertens breezes past Wang
The highlight match of the day was Muguruza facing Daria Kasatkina with the Russian having won their last two meetings, although the Spaniard would prevail 7-5, 5-7, 6-3 in two hours, 49 minutes. In what would typify the match, Muguruza jumped out to a 2-0 lead only to see the Russian take three straight games.
Winning 12 of the next 14 points, the Australian Open finalist raced to a 5-3 advantage, failed to serve out the set at 5-4 only to claim it two games later after Kasatkina double-faulted to bring up set point, followed by a forehand that went long to give Muguruza the early edge.
A 15-minute hold to open the second set and saving five break points in the fifth game with sharp play from all over the court put the Spaniard ahead 3-2. She got to 5-2 and eventually served for the match, but a double fault put the set back on serve.
Combining her offensive and defensive skills, the world number 71 won five games on the trot to force a deciding set. Seven straight breaks in the third set were sandwiched around holds in the first and last games by Muguruza, which proved to be the difference.
Mertens had little issues in getting her title defense off to the best possible start, cruising past Qiang Wang 6-1, 6-2. The two had played last week in Dubai with the Belgian taking that one 6-3, 6-0. "I tried to adapt to the wind", she said following her victory.
"You can't always play full force when the wind is coming, it changes directions. So I think that's what I managed better at last week and this week."
Kuznetsova, Ostapenko also move on
Former finalists Svetlana Kuznetsova and Jelena Ostapenko also progressed to the second round. The Russian eased past Turkish wild card Cagla Buyukakcay 6-2, 6-2 while the Latvian won the final three games of an up-and-down affair with Jil Teichmann by a 7-5, 2-6, 7-5 scoreline.
Winning by identical 6-3, 6-1 scoreline were Bernarda Pera and Karolina Muchova. The American saw off Caroline Garcia to advance to face third seed Karolina Pliskova while the Czech got the better of Hua Hin champion Magda Linette to book a second round date with seventh seed Kiki Bertens.
Siegemund, Jabeur among remaining winners
Veronika Kudermetova slipped past Kristina Mladenovic 7-6, 0-6-3 to reach round two where she will face fourth seed Belinda Bencic while Amanda Anisimova is through to meet fifth seed Elina Svitolina after a 6-3, 7-6 victory over Ekaterina Alexandrova.
Finally, Ajla Tomljanovic won the battle of Australians as she ousted qualifier Priscilla Hon 6-2, 6-4. She will next play Muguruza in a repeat of their second round match in Melbourne, won by the Spaniard in three sets while Alison Van Uytvanck blew by Polona Hercog 6-2, 6-2.