After dropping the opening set, the third seed breezed to a 3-6, 6-3, 6-0 victory against Reilly Opelka to reach the second round after 89 minutes. Monfils played well under pressure throughout his debut performance at the ATP 250 event, saving nine of 10 break points to record his 16th victory in 19 tour-level matches this season.
The 32-year-old, who captured his eighth ATP Tour title at the ABN AMRO World Tennis Tournament earlier this year (d. Wawrinka), was making his first appearance since the BNP Paribas Open in March. Monfils was forced to withdraw from back-to-back ATP Masters 1000 events in Miami and Monte-Carlo due to a left achilles injury.
In the opening match on Estadio Millennium, Portuguese qualifier Joao Domingues became the lowest-ranked Estoril quarter-finalist in the tournament’s five-year history. The World No. 214 was leading John Millman 6-3, 2-1, when the Australian was forced to retire.