John Isner started his Miami Open title defence with a tough win, while Dominic Thiem and Kei Nishikori bowed out on Friday.
Isner, the defending champion at the ATP 1000 event, was pushed before advancing after two tight sets.
But top-five seeds Thiem and Nishikori made second-round exits, the latter's defeat continuing what has been a difficult few weeks.
Meanwhile, Novak Djokovic had no troubles as a trio of young guns progressed.
ISNER SERVES WAY PAST SONEGO
Isner, 33, was a surprise champion last year and he needed 20 aces to get past Lorenzo Sonego 7-6 (7-2) 7-6 (9-7).
The American lost just 11 points on serve on his way to reaching the third round, where Albert Ramos-Vinolas awaits.
While Isner is the defending champion, Djokovic is an equal record six-time winner of the men's singles in Miami.
The world number one made a strong start to his bid for a seventh crown by beating Bernard Tomic 7-6 (7-2) 6-2.
NISHIKORI, THIEM EXIT
The 2016 runner-up, Nishikori departed after going down to Dusan Lajovic 2-6 6-2 6-3.
Since winning the title in Brisbane and making deep runs at the Australian Open and in Rotterdam, Nishikori has made early exits in Dubai, Indian Wells and Miami.
Thiem, meanwhile, was unable to back up the biggest title win of his career after his success at Indian Wells.
The Austrian third seed was beaten 6-4 6-4 by Hubert Hurkacz, who already has two wins over Nishikori this year.
YOUNG GUNS SHINE
Hurkacz will next face qualifier Felix Auger-Aliassime, who is enjoying a breakout year and beat 29th seed Marton Fucsovics 6-4 4-6 6-0.
Seeds Borna Coric and Nick Kyrgios also got the job done in the second round.
Coric overcame Roberto Carballes Baena 7-6 (9-7) 0-6 6-2, while Kyrgios was too strong for qualifier Alexander Bublik 7-5 6-3.