Juan Martin del Potro set up a clash against Roger Federer at the Miami Open, while Alexander Zverev also advanced.
Returning Argentinean Del Potro overcame countryman Guido Pella, while Zverev needed two tie-breaks against a wildcard.
Fernando Verdasco was also among the winners in Florida, with no seeds in action at the ATP 1000 event.
DEL POTRO, ZVEREV ADVANCE
Del Potro, in his third tournament back, was too good for Pella 6-0 7-6 (7-4) and was not broken in the first round.
Talented German Zverev was forced into a battle by 18-year-old Michael Mmoh, completing a 7-6 (7-3) 7-6 (7-4) win.
Verdasco survived a tough encounter against Gilles Muller, winning 7-6 (7-2) 6-3 against his fellow left-hander.
EDMUND, POSPISIL FIGHT
Kyle Edmund needed four match points to close out a 6-4 5-7 7-6 (8-6) win over Czech Jiri Vesely.
Vasek Pospisil took two hours, 36 minutes to beat Diego Schwartzman 2-6 6-3 7-6 (7-4).
DEL POTRO CONTENT
"6-0 was not the reality of the match," Del Potro said.
CORIC, SEPPI IN ACTION
Most eyes will be on the women's draw on Thursday, but Croatian teenager Borna Coric is in action against Denis Istomin. Andreas Seppi and Donald Young open the day on the main court.