Americans John Isner and Steve Johnson haven't allowed poor weather to derail their advance at the Cincinnati Open.
Isner powered his way past Italian Fabio Fognini 6-3 6-2 on Tuesday, while Johnson, fresh from his doubles bronze at the Rio Olympics, defeated Argentine Federico Delbonis 6-4 7-5 to reach the second round of the Masters 1000 event.
US teenager Jared Donaldson is threatening to join them after claiming the first set 6-2 against world number four Stan Wawrinka.
The 18-year-old wildcard twice broke the second seed, helped by a rash of unforced errors from Wawrinka before he swept the first three games of the second set.
Play was then called for the day with the return of rain.
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Wet conditions through the day and into the night plagued the hardcourt run-up to the US Open, leaving four men's matches and three women's contests still to finish to complete the first round.
Double Olympic gold medallist Andy Murray is waiting to face the winner of a match between Juan Monaco of Argentina and Ivo Karlovic of Croatia. Monaco leads 6-4 5-3.
Australians scheduled to play second round matches at the resumption include John Millman against Domic Thiem, Nick Kyrgios who takes on Croat Borna Coric and Bernard Tomic opposite David Goffin.
American Johnson told Tennis Channel it had been a stop-start day.
"I can't keep track of how many times we stopped and started and warmed up," he said.
"But I'm super happy to come out and get the win."
Another US teenager tasted defeat as Russian Mikhail Youzhny dismissed 18-year-old Taylor Fritz 6-1 6-3.
The Russian qualifier advanced to a second-round match against Japan's Kei Nishikori.
Gael Monfils of France, seeded ninth, beat Spain's Pablo Carreno Busta 6-3 6-4, while his 13th-seeded compatriot Richard Gasquet battled past another Frenchman, Adrian Mannarino 7-6(2) 3-6 6-1.
