The world No 1 won 6-4 6-4, breaking serve once in each set to clinch victory in 85 minutes and book her spot in the semi-finals of the hard court event.
However, world No 125 Watson gave a good account of herself and had chances to break in each set.
After losing her own serve in the seventh game of the opener, the 24-year-old came close to breaking back immediately when she led 40-15 on the German's serve.
