But Schmidt is convinced that Sexton, who arrived at last year's World Cup as Ireland's first choice out-half but left New Zealand as O'Gara's replacement, will prove his doubters wrong.
"He's a super player," said Schmidt. "On top of his game he's as good as anyone, certainly in the northern hemisphere.
"I'm always delighted to see Jonny selected and getting the opportunity at the highest level."
There are concerns over Sexton's decision-making after his failed attempt at a penalty from inside his own half with seven minutes remaining.
But Sexton's Leinster teammate Ian Madigan believes the fly-half is capable of kicking such long-range efforts having practiced with him in training for the Dublin side.
"Jonny's a very accomplished kicker," said Madigan. "I know he came in for a lot of criticism on Sunday, but he knows exactly how far he can hit the ball from and, in my view, he can probably hit them from 55 metres.
"Before he took the kick, watching at home, I thought he was going to get it so it was well within his range."