AUSTRALIAN star Jarryd Hayne was trending on Twitter in the US yesterday after two brilliant punt returns in an NFL pre-season match, but the San Fransisco 49ers still have a few things to learn about their new man from Downunder.

While Hayne was lighting up social media after producing some exhilarating kick-returns in the first quarter, the 49ers' official Twitter feed sent an online shout-out to Australia.

The trouble is, they posted the wrong flag in their tweet.

But they got it right in the end.

Hayne, who was the focus of pre-game television hype, wasted no time in putting his stamp on the home game against the Dallas Cowboys, taking a punt while running backwards over his shoulder and then turning up field for a classy 27-yard return after the opening Cowboys drive.

Proving he's no flash in the pan the former rugby league star then backed it up with a 34-yard run on the next Dallas punt and was only stopped from running the length by Cowboys punter Chris Jones.

When the 27-year-old rookie took his third return for another 23-yard gain commentators gushed: "Going to be hard not to put that guy on this football team."