But last year's runner-up Jarkko Nieminen crashed out despite winning the first set against Denis Istomin. Istomin fired 10 aces and won 6-7 (5), 6-3, 6-2 to even his career record against Nieminen at 3-3.
A former top 10 player, Monaco has struggled with a right-wrist injury and has fallen to No. 54.
But he easily disposed of Becker, who is not comfortable on clay.
Monaco says that as defending champion in Duesseldorf he feels "comfortable here, everything is familiar."