Del Potro beat Lukasz Kubot 6-4, 6-2 by winning two-thirds of the points on serve and saving all four break points he faced. Kubot won a solid 61 percent of the points on serve but del Porto was able to cash in half of his six break-point chances.
Third-seeded Richard Gasquet was on the court just 55 minutes in routing Fabio Fognini. He lost 10 points over eight service games.
But Bobby Reynolds ousted second-seeded John Isner 3-6, 6-4, 6-3. Isner characteristically had 20 aces but uncharacteristically had his serve broken three times.
Also, Julien Benneteau took out fourth-seeded Feliciano Lopez 6-3, 6-4; Alex Bogomolov Jr. was a 7-6 (7-5), 6-4 winner over No. 5-seeded Viktor Troicki; and Jarkko Nieminen eliminated eighth-seeded Radek Stepanek 6-7 (7-5), 7-5, 1-6.
Del Potro goes against Baghdatis and Benneteau plays Bogomolov in the quarterfinals of the top half of the draw. Gasquet meets Istomin and Nieminen draws Reynolds in the other half.
Swim Week Miami Beach 2014 [PHOTOS]