Keys is expected to be the aggressor on Arthur Ashe Stadium against a more defensive Stephens, one of the best retrievers on the tour.
"It will be an interesting match because they have two completely different styles," Wilander, in Flushing Meadows as an analyst for Eurosport, said in his daily chat with Reuters on Friday.
"It's hard to know if Stephens is quick enough to stay in the rallies for long enough and it's hard to know if Keys will keep away from missing after four or five shots if the ball keeps coming back."
Nerves, the Swede believes, will play an important role as the pressure will be sky high on two players on their home turf.
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But it is Keys's game that could be more affected.
"I would think the pressure is on Madison Keys because she's lately been playing better and been in the top 10 this year," said Wilander, who won the U.S. Open in 1988.
"It's much harder to play when you are the one who is going to be aggressive, it's harder to play because you're the one who has to make the choices, while Stephens will be here to survive."
Stephens, recently back from a foot injury that kept her from the courts for a year, showed her defensive prowess in her defeat of Venus Williams, while Keys hit winner after winner to crush compatriot CoCo Vandeweghe in the other semi-final.
"It's going to be a great match. They know each other very well, they practise together and I'm assuming they're good friends. They're both going to be nervous, I think," said Wilander.
"Playing the final of the U.S. Open, for them it means more pressure.
"It will affect the game for sure but it doesn't mean it's not going to be a high level.
"Keys will be more careful and it could help her, and people are going to see longer rallies."
(Reporting by Julien Pretot; Editing by Ian Ransom)
