Federer wowed a boisterous, capacity crowd at Crandon Park, winning 6-3 6-4 in just over 80 minutes of nearly flawless tennis.
Former US Open champion del Potro, buoyed by a large Argentine contingent who did their best to lift him with regular chants of 'ole, ole, ole', did not submit easily but one break in each set was enough for Federer to move on to the fourth round.
“Shortly before I walked to the court, you could sense the atmosphere,” Federer told the Miami Herald. “I think if the match would have gone three sets or tiebreakers or something even closer, it would have been really epic.”
Federer improved his career record against del Potro to 16-5, the Swiss closing out the match in style with a forehand winner before acknowledging the roaring crowd.
The 35-year-old, who missed the second half of 2016 with a knee injury, has lost only once this year, to Russian Evgeny Donskoy in early February.
An 18th grand slam crown in a five-set thriller over long-time rival Rafa Nadal at the Australian Open in January has been the highlight of the still young season, but the past two weeks in the United States have been second to none.
He ripped through the field at Indian Wells without dropping a set en route to the title, and has not lost a set in his first two matches in Miami either.
Federer is giving his opponents less time than ever to react, running them ragged by regularly standing inside the baseline and taking the ball early.
Next up for Federer is Spanish 14th seed Roberto Bautista Agut, who overcame a slow start to outlast American 22nd seed Sam Querrey 3-6 6-2 6-3.
Czech 10th seed Tomas Berdych beat 24th seed Gilles Muller of Luxembourg 6-3 6-4, while Adrian Mannarino of France edged Croatian Borna Coric 6-4 2-6 7-6(3).
In late matches, top seed Stan Wawrinka beat Malek Jaziri 6-3 6-4 as he tries to capture his first tournament of the year. Wawrinka will face German Alexander Zverev after the 19-year-old beat American John Isner 6-7(5) 7-6(7) 7-6(5) in a thriller. Isner served 28 aces but still came up short.
Nick Kyrgios came out on top after a battle with Ivo Karlovic, the Australian winning 6-4 6-7(4) 7-6(2) to set up a meeting with 8th seed David Goffin, who beat Diego Schwartzman 4-6 6-3 7-5.
RESULTS FROM THE MIAMI MEN'S SINGLES ROUND THREE
1-Stan Wawrinka (Switzerland) beat Malek Jaziri (Tunisia) 6-3 6-4
4-Roger Federer (Switzerland) beat 29-Juan Martin Del Potro (Argentina) 6-3 6-4
Adrian Mannarino (France) beat Borna Coric (Croatia) 6-4 2-6 7-6(3)
14-Roberto Bautista (Spain) beat 22-Sam Querrey (U.S.) 3-6 6-2 6-3
10-Tomas Berdych (Czech Republic) beat 24-Gilles Muller (Luxembourg) 6-3 6-4
8-David Goffin (Belgium) beat Diego Schwartzman (Argentina) 4-6 6-3 7-5
16-Alexander Zverev (Germany) beat 18-John Isner (U.S.) 6-7(5) 7-6(7) 7-6(5)
12-Nick Kyrgios (Australia) beat 17-Ivo Karlovic (Croatia) 6-4 6-7(4) 7-6(2)
Read the original article on Eurosport: Federer eases past Del Potro in Miami