Pika and Goliath! - S11.E22

Ash and his friends meet Sho, a boy who has a Pichu and a Raichu. He mistakes Ash's Pikachu for a wild Pokémon. Just like at the Vermillion City Gym, Ash and Pikachu have the option again to evolve Pikachu to Raichu, after a loss to a stronger opponent. Paul witnesses this defeat and scolds Ash for losing to such an opponent, but manages to redeem himself of that defeat in a rematch.