The Russian's return to the big stage had been eagerly anticipated and her opening win against second seed Simona Halep prompted pundits to rate her among the favourites at Flushing Meadows.
But her run ended with a 5-7 6-4 6-2 defeat to Latvian 16th seed Anastasija Sevastova at Arthur Ashe Stadium.
"To be able to come back and play like she played is impressive but unfortunately when you go back you see she was not doing that well on tour since a couple of years before her suspension," former U.S. Open champion Wilander, at the U.S. Open as an analyst for Eurosport, said in his daily chat with Reuters.
"I think I made a mistake, it's not right for everybody to think she could have returned to a place where she was six or seven years ago."
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Sharapova, who won her last grand slam tournament at the 2014 French Open, failed her drugs test at the 2016 Australian Open.
"She was not really playing that well before she got back from suspension. Why? Maybe she was lacking a bit of that Sharapova fire, like she was not as determined today," said Swede Wilander.
"On a few points I was a little bit surprised. I thought it was surprising that she did not win this match but then I remembered how she was playing before her ban.
"She never gave up but there was a little bit of confidence missing."
Wilander said the former world number one had brought a lot to the U.S. Open, her presence in the main stadium in her four matches making sure the 23,771 seats would be taken.
"(They were) great matches for her on Arthur Ashe, four matches in a row," said Wilander.
"What is cool about Sharapova is that she was not down after making a mistake, everybody makes mistakes. She was an inspiration for the tournament."
(Reporting by Julien Pretot; Editing by Ian Ransom)
