The match lasted only an hour and 12 minutes, with Del Potro absolutely dominating from the moment he walked on the court.
Nishikori was only able to hold his own for four games, as Del Potro broke for 3-2 in the first and then cruised to the win from there.
This match was obviously lopsided in a number of different ways, but serving was a huge reason that the Argentinian won the way he did. The world No. 6 won 77 percent of points on both his first and second serves, and Nishikori was far from that level of efficiency. The former world No. 4 won only 56 percent of his first serve points, and it was an even lower 45 percent on his second serve.
Match point from Del Potro's win over Nishikori in Miami:
It's hard to really get on Nishikori's case about this match, as he is far from 100 percent right now. Nishikori has been dealing with a serious wrist injury since Wimbledon, and will need to work on his match conditioning.
Del Potro, meanwhile, is arguably playing the best tennis of his life. The 29-year-old is coming off of a title win in Indian Wells, and, despite being tired, he could complete the Sunshine Double in Miami.
Del Potro's forehand has always been as dangerous a weapon but left wrist surgeries have weakened his backhand in recent years, forcing him to hit more slices than two-handed shots. So far in 2018, though, his backhand is not the weak link it once was, which has made all the difference for him.
Del Potro's next opponent in Miami will be 26-year-old Filip Krajinovic, who beat Benoit Paire 6-3, 6-3 on Sunday.
For a limited time, use promo code "WTA20" for a discount on Tennis Channel Plus—where you'll find the following:
WTA Miami (March 20-April 1)
-Tennis Channel Plus has Miami Open covered with up to 7 WTA courts, catch all the action live beginning Tuesday, March 20
WTA Indian Wells On-Demand
-Watch your favorite WTA matches from Indian Wells on-demand on Tennis Channel Plus