A method and circuit for implementing enhanced diagnostics with intelligent pattern combination in automatic test pattern generation (ATPG), and a design structure on which the subject circuit resides are provided. A random fault is selected in the design. A test pattern is generated and applied the test pattern to a design under test to test the selected random fault. The test is re-simulated to determine faults that are covered by the applied test pattern. A next iteration of test pattern generation includes selecting a fault that is based upon the previous test pattern generation for generating new test patterns.