Stan Wawrinka continued his good form by reaching the Mexican Open second round, while Steve Johnson also advanced on Monday.
Wawrinka, a three-time grand slam champion who has battled injuries in recent years, beat American qualifier Ryan Harrison 6-4, 7-6 (8-6) in Acapulco.
The Swiss star is coming off a run to the final in Rotterdam earlier this month and served nine aces in his win over Harrison.
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Wawrinka will next face Johnson after the American seventh seed got past wildcard Gerardo Lopez Villasenor 7-5 7-5 at the ATP 500 event.
Australian eighth seed John Millman also progressed after a 6-3 6-4 win over qualifier Marcel Granollers.
Millman's next opponent is Peter Gojowczyk, who battled past Federico Gaio 5-7 6-4 6-2.
In the day's final match, sixth seed Frances Tiafoe rallied to overcome Jordan Thompson 3-6 6-4 6-3.
At the Brasil Open, Lorenzo Sonego, Christian Garin, Marco Trungelliti and Roberto Carballes Baena enjoyed first-round wins.
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