McMahon challenges established order
But such is the Wallabies' embarrassment of back row riches, the 21-year-old Melbourne Rebels player faces a fight for inclusion in the matchday 23 at Twickenham on Saturday.
McMahon was the star performer as the Wallabies crushed Uruguay 65-3 to go top of Pool A ahead of Wales.
The flank opened the scoring with a neatly taken peel-away try off the back of a dominant maul. He sealed his brace in similar fashion in the second half.
But it was more his abrasive free-running role in midfield and constant harrying of the Uruguayan half backs that caught the eye in a vintage openside flank's masterclass.
"It's pretty exciting," McMahon said after picking up the Man of the Match award.
"It's my first World Cup game. It's like dreams are becoming reality for me, and now to get to the World Cup and get a Man of the Match performance in front of such a great crowd is unbelievable."
But Australia have inestimable strength in the back row.
Against Fiji, coach Michael Cheika opted for two opensides in Michael Hooper and David Pocock, complimented by the rugged Scott Fardy at blindside.
That trio bonded fantastically, Pocock driven over for two tries in an outstanding performance.
With two-try Ben McCalman also playing well on the blindside against Uruguay, Cheika will have a lot to ponder ahead of the final pool matches against England and Wales, both at Twickenham.
"There's a few players that definitely put their hand up for selection," said Cheika.
"In the areas I wanted those players to make an improvement in, in particular. We'll make an assessment this afternoon about our selections going forward."
"It's getting a bit ridiculous really because every Man of the Match is seven or eight. Sean McMahon's initial selection was for a certain reason and he's certainly bringing that and he's fulfilling his role within the team, and when he gets his opportunity to play for Australia he needs to cherish that because not everyone gets that chance.
"We've got some pretty influential players in those positions, but as long as he's there rattling their cage, that will keep them honest and that will keep him honest as well going forward.
"I was very pleased and proud of his performance because he knows those guys are there and he's just got to keep taking it to them."
Prop Scott Sio said the fact that the Wallabies had put out two different teams for their two games was great for competition for places.
"I think that's what the two months in the Rugby Championship were all about, building that depth in each position," Sio said.
"No one has a lock on any position. Anyone could play there and we know they'd get the job done. Some of the guys that didn't play in the first game really stepped up and played well today."
AFP
