You will actually fight two Dr. Wiley's; The first one is a robot Dr. Wiley piloting a large crab-like robot. The second Dr. Wiley is the one this hint is concerned with.

First, you'll see a large robot body filling up the background. A blue robot head should rest on top. Fire Shadow Blade straight up to quickly defeat the robot head. Dr. Wiley should appear.

When the robot attempts to punch MegaMan, jump on to the hand. Then, jump to the small nearby platform. Jump off of the platform directly at Dr. Wiley and use Top Spin right at contact. A direct hit and the game is over -- you win!