Didier Deschamps believes Kylian Mbappe is set for another memorable World Cup after he claimed a goal and an assist in France's 4-1 win over Australia, declaring: "It's his competition".

Mbappe became just the second teenager – after Pele in 1958 – to score in a World Cup final as France downed Croatia to win the tournament in Russia four years ago, and he made a strong start to this year's competition as Les Bleus claimed a comeback win.

Craig Goodwin handed Australia a surprise lead in Tuesday's Group D clash, but Mbappe built on first-half strikes from Adrien Rabiot and Olivier Giroud as France got off to a winning start.

At 23 years and 337 days old, Mbappe is now the youngest player to have scored five World Cup goals for France, and Deschamps expects him to go from strength to strength in Qatar. 

"Kylian has been one of the best players in the world for some time now, and he's feeling very confident," Deschamps said. "You can see that in the way he plays. He is calm and concentrated. 

"He has been in good form for quite some time. I knew he was going to be ready for this World Cup, it's his competition and he knows how to make the difference.

"He's always been able to play as part of a team, so that's great for us, and I've got a lot of attackers, but Kylian is, of course, an outstanding one."

France's victory ensured they became the first World Cup holders to make a winning start at the tournament since Brazil did so in 2006, while their current five-match winning run at the finals is their joint-longest such streak (also five across the 1986 and 1998 editions).

However, France's win was tarnished as they received yet another injury blow, with Bayern Munich's Lucas Hernandez limping out of the game in the aftermath of Australia's early goal.

Deschamps fears the defender may have sustained a serious injury, which could open the door for his brother Theo Hernandez to start Saturday's fixture against Denmark.

"With Lucas Hernandez, we're still waiting for the results of the tests, but I'm afraid it could be pretty serious," Deschamps said.

"It's true that Lucas' injury was a tough blow. I'll have to think about his replacement.

"You can't have three players for every position in your squad, but there is obviously Theo Hernandez and other alternatives."