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Serena Williams was reportedly "worried" about bestie Meghan Markle's presence at her U.S. Open championship match against Canadian tennis phenom Bianca Andreescu, 19.

Bianca beat Serena in straight sets 6-3, 7-5 to win her first ever major title.

Meghan flew to New York City on a budget commercial airline to watch her bestie try to win her 24th Grand Slam title in the U.S. Open women's final on Saturday.

Serena's camp was reportedly "concerned" that Meghan's presence would be a bad omen for Serena, who loses whenever Meghan watches her play.

According to Page Six, Serena, who turns 38 this month, asked her coach, Patrick Mouratoglou, if the Duchess should attend the women's final because Serena is "superstitious".

"Serena asked her coach about Meghan coming when she won last night and everyone is worried, as tennis players are very superstitious, and Serena lost when Meghan came to watch her at Wimbledon," a source told Page Six.

A separate source told Page Six, "Serena adores Meghan and she's so excited about her coming to the Open."

But Serena is reportedly so superstitious that she wears the same dirty socks every day of a 2-week tennis tournament.

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Serena's coach (pictured in the player's box with Meghan on Saturday) said Meghan's presence at the Open would not be a distraction for Serena.

"There will be 22,000 people in the stadium, 23,000, actually. One more or less won't change a thing."

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Serena has not been herself since giving birth to daughter Alexis Olympia Ohanian Jr., 2 years ago.

She reached four major finals since becoming a mother - Wimbledon twice and the US Open twice - but she lost all four times to much younger opponents.

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Mouratoglou practically guaranteed Serena would beat Andreescu. He said Serena is not the same woman who lost to 20-year-old tennis prodigy Naomi Osaka at last year's US Open.

"It's totally different situation now, because now she can move," said Mouratoglou of Serena.

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Mouratoglou blamed Serena's losses on motherhood. Daughter Alexis Jr. is pictured above with Serena's husband, Reddit.com co-founder Alexis Ohanian in January.

"The first problem she had was not an injury, but her body transformed to become a mother," he said. "You don't come back to your previous body, which is the body of a professional top athlete, overnight. So that was the first goal, to be completely in shape and able to perform at the highest level physically."

"She finally got rid of her knee problem, and she was able to run without thinking about her knee. So now it's several weeks in a row, so I think her fitness just went up and up, and I think her movement now is better than I have ever seen since she became a mother."