The England midfielder, who led Madrid in scoring last season, started this campaign slowly but has netted seven goals in his last eight Spanish league games.
He notched another goal in the 63rd minute of the Super Cup semi-final on Thursday when he finally broke down a tough Mallorca side who until his goal had imposed their defensive style on the star-studded Madrid.
Bellingham blasted in the third shot in a row by Madrid after Rodrygo initially hit the post and goalkeeper Dominik Greif blocked a follow-up by Kylian Mbappé.
Bellingham collected the rebound and slotted his shot from just outside the six-yard box under the on-rushing Greif and past three defenders who were trying to protect the goalmouth.
Madrid then scored twice late in stoppage time. Mallorca's Martin Valjent scored an own goal when he inadvertently turned a pass by Brahim Díaz into his net. Rodrygo then netted Madrid's third.
The match ended with a short scuffle after the final whistle before calm was restored.
Barcelona await Madrid in Sunday's final.
Madrid lost Aurélien Tchouaméni, a midfielder playing as a central defender, in the 54th after he took a hard knock to the head during a collision with a Mallorca player. Youth player Raúl Asencio replaced him.
Madrid were competing as last season's Spanish league champions, while Mallorca were invited as the runner-up in the Copa del Rey.
Former Madrid striker Karim Benzema, who now plays in the Saudi Arabian league, was in attendance.
The minor trophy has become a major cash maker for the federation and competing clubs since the federation struck a deal in 2019 to hold it in the Middle Eastern kingdom.
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