Yeah, actually, I ran into that just the other day. Using "Sunbo" against Chuck's Poliwrath...
Sunbo, as the name suggests, Is a lvl 30 Sunkern (waiting until Ice Cave to evolve.)
While the odds of a Sunkern defeating an equal-leveled Poliwrath is about the same odds as a baby Sea turtle killing an Elephant, I decided to try and Sunny Day to use Solarbeam on it. and I swear, every time I went for a Hypnosis, or Sunnyday, or eventually just tried Solarbeaming him naturally, He called a Focus Punch.
Oddly enough, Razor leaf did the trick and one-shotted him if I recall.