Del Potro beat Federer on Sunday in a titanic three-setter in California.
The win for the Argentine, who saved three match points, ended Federer’s 17-match unbeaten streak and gave him his first ATP Masters 1000 title.
Federer is the number one seed in Miami as he looks to defend the title he won in 2017 by beating Rafael Nadal.
And as a top 16 seed, the Swiss star has a first-round bye and will play a qualifier in the second.