The Sexyback singer was taking part in a charity golf tournament with Bill Murray and swimmer Michael Phelps.
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And cheering him on from the sidelines was his gorgeous fiancée Jessica Biel.
Last week Justin bid farewell to single life in the traditional manner by taking a group of 25 of his closest friends off on a stag do.
The boys were spotted partying on Las Vegas' famous strip before they decamped to Mexico.
In Cabo, the singer-turned-actor and his crew played beach volleyball and sampled the nightlife.
Justin is due to marry his Total Recall actress girlfriend soon, though the date remains unknown.
However, the star's grandmother let slip the couple will marry in Italy.
Sandy Bomar told Star magazine that the she and her husband Bill would miss the nuptials as Mr Bomar's health problems make it too difficult to travel.
"Unfortunately, we won't be able to go to Italy," she told the publication.
The nearlyweds are expected to hold their nuptials at the Palazzo Margherita in the Italian town of Bernalda. Director Francis Ford Coppola owns the upmarket hotel and his daughter Sofia wed there.