Kessler had never defeated a top-50 opponent in her career before taking down Wang, who coughed up a 2-0 lead in the second set. Kessler also put together a strong finish, winning the final four games of the third set after Wang drew even at 2.
Despite losing, Wang still managed to finish with more aces (5-4) and fewer double faults (4-3).
Two other seeded players fell, as the Netherlands' Arantxa Rus beat Bulgarian seventh seed Viktoriya Tomova 6-3, 6-3 and France's Clara Burel got past eighth-seeded Sophia Kenin of the United States 6-4, 6-3.
Top seed Beatriz Haddad Maia of Brazil, third seed Katerina Siniakova of the Czech Republic, fifth seed Russian Anastasia Potapova and sixth seed Peyton Stearns of the United States all prevailed. Romania's Ana Bogdan also advanced.
Abierto GNP Seguros
No. 7 seed Yue Yuan of China cruised to a 6-4, 6-1 win over Croatian Petra Martic in second-round action in Monterrey, Mexico.
Yuan finished with just one ace to Martic's five but saved four of six break points and converted five of six.
Fifth-seeded Elina Svitolina of Ukraine and sixth-seeded Linda Noskova of the Czech Republic also advanced with straight-set wins.
New Zealand's Lulu Sun saved a match point late in the third set and emerged with a 6-3, 2-6, 7-6 win over Argentina's Maria Lourdes Carle.