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.

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.