He was also the star of the show when Leinster won their Amlin Challenge Cup quarter-final against Wasps but with Sexton back to full fitness, he has been moved to the centres for Saturday's semi-final against Biarritz.
But Schmidt insists it was far from a straightforward decision.
"One is the up and comer, the other has been there, done that," Schmidt told the Irish Independent.
"In finals football you want a little bit of been there, done that, but you also want a little bit of the unknown.
"Ian has probably got a bit of a change-up - you don't see Jonny score as many tries as Ian because Ian plays a little bit flatter, takes the line on in his pass delivery, in his change-up and his step and go.
"That sort of change-up when players tire is really effective, or if taken through phases early in game. He is always a running threat. That is a little bit different from Jonny, who tends to play two players around him and bring them into the game more.
"Ian certainly brings others into the game, but when defenders are not watching, he is looking to bring himself into the game."
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