Australian tennis player John Millman has made Olympic history, dishing out the Games' first double bagel to win his first-round match.

Millman, who only made the team after the withdrawals of Bernard Tomic and Nick Kyrgios, beat Lithuania's Ricardas Berankis 6-0, 6-0 in just 50 minutes.

"I'm not really sure that's sunk in," the 27-year-old said.

"To be put in the record books is ridiculous."

Millman's next match should be a tougher affair, as fourth seed Kei Nishikori awaits after beating Albert Ramos-Vinolas 6-2, 6-4.

The Australian served five aces to Berankis' zero and did not double-fault once, while his opponent failed to get a ball into play on serve six times.

But the biggest disparity was in the unforced errors, where Berankis had 27 miscues to Millman's two.

Millman, ranked 75th in the world, was the only Australian male to win on the first day of competition as Thanasi Kokkinakis and Jordan Thompson both fell short as did the doubles pairing of Chris Guccione and John Peers.

Kokkinakis battled hard but was beaten 7-6(7/4), 7-6(7/3) by Poruguese world number 61 over two hours and 12 minutes, while Thompson fell to Great Britain's Kyle Edmund 6-4, 6-2.

Argentina's Juan Martin del Potro and Maximo Gonzalez beat Peers and Guccione 6-4, 7-5.

The women's doubles did not bring much more joy for Australia with Daria Gavrilova and Samantha Stosur beaten by Swiss pair Martina Hingis and Timea Bacsinszky 6-4, 4-6, 6-4.

Australians Arina and Anastasia Rodionova also lost, falling to Russians Ekaterina Makarova and Elena Vesnina 6-1, 6-2.