Serena Williams meets Na Li on Friday in the 2013 US Open semifinals.  The match is slated for 11 a.m. ET.  Tune in to the Tennis Channel or watch the live stream HERE and HERE.

*Editor's Note: Williams vs. Li semifinals match is on Friday, Sept. 6 at 11 a.m. ET.  Visit HERE to see Serena and Venus Williams in doubles against Sara Errani and Roberta Vinci - the match doesn't begin before 12:30 p.m. ET on Thursday.

Williams has rolled through the US Open much like she rolled through every other tournament this season.  Williams, 31, cruised through her first five opponents in New York without dropping a single set.  She's admitted everything else she accomplishes now in her career is a bonus, but she's not playing like it.

She isn't playing like her age, either.

"Mentally, she's different.  She really wants it," Patrick Mouratoglou, Williams coach since last June, told NY Daily News.  "She's working like she's 19 years old and wants to win her first Grand Slam.  She has the same appetite.

"That makes a huge difference.  How many players being (almost) 32 have the same appetite and especially after winning so many Grand Slams?  I mean, they are different.  Serena is really different, mentally."

Even more astounding, the reigning US Open champion has dropped just 13 games through the first five rounds at the US Open, according to The News.

"She doesn't speak about it," Mouratoglou said.  "What she says is she wants to be the best she can be.  She wants to keep on improving.  She said to me at the start, 'I'm prepared to do anything to be back to the top and to be winning Grand Slams.'"

Li is the last obstacle in William's way to earning a spot in the final.  Li, ranked No. 6 in the World, is 37-11 on the year with the Shenzhen Open title to her name.  The 31-year-old has played well in this year's US Open - she dropped her first set in the quarterfinals against Ekaterina Makarova.

Williams has won eight of her 10 career matches against Li.  They last met this year at Cincinnati, where Williams won in two sets.

*Stats via WTATennis.com and MatchStat.com.