World number six Juan Martin del Potro made it 14 wins in a row by accounting for Serbian Filip Krajinovic in straight sets on Tuesday.
Angelique Kerber struggled in the Miami wind, but Sloane Stephens had no such troubled as she eased to victory in just over an hour.
Spain captain Sergi Bruguera has confirmed Rafael Nadal will be part of his team to face Germany in the Davis Cup.
Alexander Zverev rallied past Spanish veteran David Ferrer at the Miami Open, while Nick Kyrgios blitzed Fabio Fognini.
Venus Williams – a three-time winner in Miami – eliminated the defending champion following a gruelling three-set battle on Monday.
Fernando Verdasco and Thanasi Kokkinakis were involved in a verbal dust-up during their Miami Open meeting on Monday.
Grigor Dimitrov has lost four of his past five matches after going down to Jeremy Chardy at the Miami Open.
Kiki Bertens had Venus Williams on the ropes in a topsy-turvy third-round match at the Miami Open, but the veteran American prevailed.