Rodriguez set the mark in the final of the tournament with 18 home runs but Soto, who got off to a slow start, was able to best it with time to spare.
The Nationals outfielder has been under media scrutiny this week having turned down an extremely lucrative deal but he was mobbed by his team after winning the Derby.
In the opening rounds, the biggest reaction was for future hall-of-famer Albert Pujols (42), who received a standing ovation from both his opponents and from his former ball park, before beating Kyle Schwarber (29) in a sudden death swing-off. He went on to lose to Soto in the semis.
Rodriguez was lighting the early fireworks though. He hit a huge 32 home runs to see of Corey Seager (28) in the first round. Seager, himself, hit 24. In the second round, Rodriguez continued his hot streak, nailing another 31 homers to beat the double reigning champion Pete Alonso (27).
However the rookie could not go all the way as Soto took the crown after making the final last year, only to lose to Alonso.
Speaking about his win, he said: "It feels amazing. It feels tiring first of all, for all the hard work you put in, then it feels amazing.
"I just tried to square up and hit the ball because I knew I had the power to get it done."
For Soto and the rest of MLB, attention will now turn to where one of the best hitters in baseball will end up. Having rejected the contract from the Nationals, his team are willing to listen to trade offers just two weeks before the deadline. Given Soto's abilities, shown once again at the Home Run Derby, the line of suitors will be long.