Novak Djokovic was hailed as a "true champion" on Monday after his Olympic Games loss to Juan Martin del Potro reduced him to floods of tears.

The world number one was beaten 7-6 (7/4), 7-6 (7/2) by the dangerous Argentine in his first round match.

It was his second successive Olympics loss to Del Potro having also come up short in the bronze medal match at London on 2012.

As he left centre court late Monday, Djokovic saluted the crowd, pumped his chest with his fist and then the tears came.

"A human side of a champ...," tweeted former Grand Slam star Chris Evert beside a close-up video of a crying Djokovic.

"Anyone that says #Olympics doesn't mean anything to tennis players, hope you watched @DjokerNole v @delpotrojuan both in tears at the end," wrote former Australian Grand Slam doubles champion Todd Woodbridge on Twitter.

Djokovic was trying to become just the third man to complete the career Golden Slam of all four majors plus Olympic gold.

Instead, his record remains just a singles bronze from the 2008 Games in Beijing.

The Serb praised the Barra arena crowd for the standing ovation they gave him as he trudged disconsolately off court.

"I don't know how to thank them. I never felt this support before apart from in my own country," said Djokovic.

"This felt like I was in my own country. I felt like I was Brazilian and I thank them with all my heart."

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