Nishikori, Isner battle into quarter-finals
Top seed Kei Nishikori battled into the Argentina Open quarter-finals, while John Isner won through in Memphis.
In his first outing since the Australian Open, Nishikori overcame Diego Schwartzman 5-7 6-2 6-2 on the clay in Buenos Aires on Wednesday.
The Japanese star recovered from a slow start to break five times in the final two sets in the second round of the ATP 250 event.
The seeds enjoyed a good day in Argentina.
Joao Sousa beat Federico Delbonis 7-5 6-3, Pablo Carreno Busta edged past qualifier Alessandro Giannessi 6-1 4-6 6-4 and Albert Ramos-Vinolas led Leonardo Mayer 6-7 (4-7) 7-6 (7-3) 1-0 when the Argentinian retired.
Only eighth seed Paolo Lorenzi departed, the Italian losing 6-3 6-3 to Gerald Melzer in the first round.
Fresh from yet another Ecuador Open success, Victor Estrella Burgos was crushed 6-2 6-1 by Brazilian Thiago Monteiro in just 50 minutes.
On the hard courts at the Memphis Open, Isner was also forced into a three-setter by Yoshihito Nishioka in the second round.
The big-serving American second seed and 2010 runner-up eventually sent down 26 aces in a 4-6 6-3 6-4 victory.
Seventh seed and 2008 champion Steve Darcis was sent packing after a 7-6 (7-2) 6-4 loss to Damir Dzumhur.
Donald Young set up a clash against Isner in the quarter-finals by beating fellow American Reilly Opelka 7-6 (7-3) 6-3, while the third-seeded Sam Querrey, a former champion, was comprehensively beaten by Ryan Harrison 6-3 6-1.
In first-round matches, Nikoloz Basilashvili thrashed Jordan Thompson 6-3 6-0 and Mikhail Kukushkin was too good for lucky loser Benjamin Becker 6-3 6-4.