Estoril, Portugal, 30 April 2019 | AAP

Australian young gun Alex de Minaur has made a shock early exit at the ATP Tour’s Estoril Open, losing his first-round clash to lowly-ranked local Joao Domingues.

World No.27 De Minaur was upset 6-2 2-6 6-2 by Portugal’s Domingues, ranked 187 spots below his fancied opponent, in just under two hours.

De Minaur, who missed the Miami Open due to a groin injury after losing his opening match at Indian Wells, had his serve broken four times after winning less than half of the points on his second serves.

Domingues goes on to face the winner of the all-Australian showdown between John Millman and Bernard Tomic, which highlights first-round action on Tuesday.

Another Aussie, 19-year-old Sydneysider Alexei Popyrin, qualified for the main draw and will face Portugal’s Joao Sousa in his first-round match.

In other opening-round action on Monday, American Reilly Opelka, Guido Andreozzi of Argentina and Japane’s Yoshihito Nishioka all won to advance to the second round.

At the WTA tournament in Rabat, Australians Daria Gavrilova and Ajla Tomljanovic will both play their first-round matches on Tuesday.

Gavrilova takes on second seed Hsieh Su-Wei while No.4 seed Tomljanovic tackles French qualifier Fiona Ferro.