The Steel Ball Run race is officially won by Pocoloco.

Quick Scoop

In the story, Diego Brando actually crosses the finish line first and is initially considered the top finisher, but he is later disqualified for story- related (spoiler-heavy) reasons.

Because of that disqualification, the carefree, incredibly lucky racer Pocoloco is declared the final winner of the Steel Ball Run and receives first place in the race’s results.

So if you’re asking “who won the Steel Ball Run?” in terms of the canon, official results of the race, the answer is: Pocoloco.

Information gathered from public forums or data available on the internet and portrayed here.