A pair of seeds, Fabio Fognini and Florian Mayer, were among Tuesday's opening-round winners at the $530,000 Mercedes Cup tennis event.
The fifth-seeded Italian Fognini held off British qualifier Alexander Ward 6-3, 7-6 (7-5), while the sixth-seeded German crowd favorite Mayer got past qualifier fellow countryman Andreas Beck 6-4, 3-6, 6-1 on the red clay at Weissenhof Tennis Club.
A Day-2 upset came when Brazil's Thomaz Bellucci bounced seventh-seeded Czech Lukas Rosol 6-4, 6-4.
Also on Tuesday, Latvian Ernests Gulbis fought back to beat Spaniard Marcel Granollers 4-6, 6-1, 6-1; 2009 runner-up Victor Hanescu of Romania saved two match points before overcoming Russian Dmitry Tursunov 3-6, 6-3, 7-6 (9-7); Russian Nikolay Davydenko came back to beat Spanish qualifier Daniel Munoz-De La Nava 6-7 (6-8), 6-3, 6-4; 2010 Stuttgart runner-up Gael Monfils topped fellow Frenchman Paul-Henri Mathieu 7-6 (7-0), 6-4; qualifier Nils Langer downed wild card and fellow German Robin Kern 3-6, 6-4, 6-3; and Argentine Leonardo Mayer outlasted Spaniard Pablo Andujar, the 2011 Stuttgart runner-up, 3-6, 7-6 (7-5), 7-6 (7-5). Gulbis will battle 1999 Stuttgart titlist Tommy Haas on Thursday.
This week's big winner will take home $110,000 and a brand new Mercedes-Benz sports car.