Juan Martin del Potro and Milos Raonic moved into the Delray Beach Open second round with straight-sets wins on Tuesday.
Del Potro, the 2011 champion and second seed in Florida, eased past Jeremy Chardy 6-2 6-4 at the ATP 250 event.
The 2009 US Open winner dropped serve once, but he managed to break his French opponent four times.
Raonic, who underwent wrist surgery in 2017, claimed his first ATP World Tour win of the year, the Canadian ninth seed beating Taro Daniel 6-1 7-5.
Last year's runner-up at Delray Beach, Raonic will next face Steve Johnson after the American beat Nikoloz Basilashvili 6-3 6-4.
Of the four seeds in action, three advanced as John Isner joined Del Potro and Raonic in the second round, serving 21 aces in a 5-7 6-3 6-4 victory over Radu Albot.
Next up for Isner is Peter Gojowczyk, who claimed a 3-6 7-5 6-1 win over Lukas Lacko.
Sam Querrey – the fourth seed and a finalist at the New York Open – fell, edged by Taylor Fritz 2-6 6-3 7-6 (7-4).
Awaiting Fritz in the second round is Mikhail Youzhny, who won a battle of veterans against Dudi Sela 7-5 6-4.
Canadian teenager Denis Shapovalov beat Ivo Karlovic 7-5 7-6 (7-4) and Franko Skugor was too good for Alexander Bublik 6-2 7-5 in a clash between two qualifiers.
Reilly Opelka sent down 15 aces in a 7-6 (7-5) 7-6 (8-6) win over Ryan Harrison, Evgeny Donskoy brushed past lucky loser Darian King 6-4 6-2 and Jared Donaldson got past Peter Polansky 7-6 (8-6) 6-1.
