Kohlschreiber didn't manage a break point in the first set but posted a pair of breaks in each the second and third sets of a 3-6, 6-3, 6-3 win over Haas. After evening the match with the second-set win, Kohlschreiber dropped only five points on serve in the final set.
Haas was coming off a tournament win Sunday at the Erste Bank Open in Austria.
Defending champion David Ferrer, who is also the No. 1 seed for the tournament, routed Gael Monfils 6-3, 6-2 in 62 minutes during a first-round match. Ferrer saved two of the three break points he faced and ended up winning three-quarters of the points on serve.
Seventh-seeded Fabio Fognini beat Marcel Granollers by the same 6-3, 6-2 score but in a quicker 59 minutes. Fognini, like Ferrer, had two breaks in each set of a second-round battle.
Also in the second round, Dmitry Tursunov ousted Roberto Bautista Agut 6-2, 7-6 (7-3). He had 11 aces, but also seven double faults, in winning more than 60 percent of the points on serve.
Other first-round results Wednesday saw fourth-seeded John Isner edge Ernests Gulbis 7-6 (7-4), 7-6 (7-2); Jeremy Chardy beat Florian Mayer 4-6, 7-5, 6-3; and Jarkko Nieminen taking out Benoit Paire 6-3, 6-3.