The Court of Arbitration for Sport said Sharapova was not an "intentional doper" and hence they reduced her ban to 15 months.
From 1-4 down in the second set, Halep reeled off five straight games, saving numerous break points to serve out the second set 6-4.
Sharapova will now face unseeded Hungarian Timea Babos in the second round.
Sharapova made a triumphant comeback to the major scene after upstaging second seed Halep 6-4 4-6 6-3 in the opening round of the US Open at Flushing Meadows on Monday. The French Open denied her a wildcard and she missed Wimbledon with a thigh injury, setting the stage for a US Open wildcard organizers defended by saying she was being treated like several past US Open champions. She then cited the same problem as reason for withdrawing from Toronto and Cincinnati as she sought reassurance from specialists that she would be able to play here in NY.
With the U.S. Open draws ravaged by injuries and withdrawals, Sharapova provided a splash of glitz and glamor to the tournament strolling onto the floodlit court like it was catwalk in a jet black tennis dress that sparkled with Swarovski crystals. Her five major championships include the 2006 U.S. Open.
There is undoubtedly a pressure to try to live up to the ranking and for Pliskova that means attempting to go one better than past year at Flushing Meadows, when she lost to Angelique Kerber in her first grand slam final.
The 30-year-old Russian admitted that she was nervous to face the in-form Halep. Sharapova returned from a 15-month doping ban in April.
This loss drops her to 0-7 in matches against Sharapova, including a loss in the 2014 French Open final between the two stars.
The stakes of the match were higher for Halep.
As well as vying for the title over the next fortnight, the world number one spot is also in reach for eight players - strength in depth that King is delighted to see after Williams' recent dominance. For Halep, the defeat is another lost opportunity that stings. This time, however, Halep could not dig herself out of an early deficit. As a method of self-preservation as much as anything, she has since tried to put that summit out of her mind.
"But of course it's not so easy".
"Prime time baby", screamed Sharapova, now 18-0 in night time matches on Arthur Ashe. The third set began like the first two.
Muguruza and Sharapova aren't the only women with a shot to win the title.
"My reaction was normal, because this year I had very tough draws every time, almost", Halep said when asked about the draw. "In fact, ten to 12 of them can succeed at the US Open", the Russian tennis federation president noted.
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