— -- NEW YORK -- For months, Serena Williams has handled the building pressure as she won match after Grand Slam match. On Friday, her mother, Oracene Price, said the pressure likely got to the top-seeded American as she lost her bid to complete a calendar Grand Slam with her semifinal defeat at the US Open.

"Yes, [from] everybody," Price said on whether the attention might have finally become too much for her daughter. "Of course, then the pressure you put on yourself." 

For her part, Serena rejected the notion that she felt pressure in her postmatch news conference. 

"I told you guys, I don't feel pressure. I never felt pressure," Williams said. "I don't know. I never felt that pressure to win here. I said that from the beginning."

But Serena's mother said she noticed her daughter was off her game from the moment the match began. Serena had done well managing the pressure as she won four straight Grand Slam events but didn't have her usual confidence against unseeded Italian Roberta Vinci, losing 6-2, 4-6, 4-6.

"Every day things can be different," Price said. "Just little things can put seeds of doubt in your mind and then you think too much, don't do what you should do, when you're out competing."

After the match, Serena went straight to the locker room while her family gathered in the hallway outside. There, Price, Serena's sister Venus Williams and other members of the family's inner circle hugged and spoke in hushed tones.

"I just feel for her because I know she wanted it and couldn't play her best; that's disappointing," Price said. "I think she was just really tight and couldn't muster through it today." 

Serena's coach, Patrick Mouratoglou, said Serena didn't move as well on the court as she had even during matches where she struggled, losing a set to Bethanie Mattek-Sands in the third round and one to her sister Venus in the quarterfinal.

"I could feel it since the morning she was not having a good day," Mouratoglou said. "And it's not about the semis because yesterday she had a good day. There are sometimes bad days during the Grand Slams and it's about [finding] a way through, and she didn't find a way through today."

The semifinals were initially scheduled to be played Thursday night, but a rainstorm and a half-finished roof combined to cancel the evening session and the women's semifinal matches were rescheduled for Friday. Mouratoglou speculated that having to go from a match against Venus to playing Vinci might have led to an unintentional letdown. Williams had a 4-0 advantage over Vinci until losing the semifinal Friday.

"Maybe to play a player like Venus and then Vinci is difficult," he said, "because she has to take her A-game against Venus and then she doesn't feel the same pressure that she has to. It's not about not respecting Vinci, but she has this record against her every time she plays her, she wins in two sets. It's not conscious, but you don't come to the court with the same intentions and then she didn't feel well today, so the combination of those two things made her not be aggressive enough mentally."