Serena Williams set up a US Open final rematch against Victoria Azarenka by powering past Li Na.
The world number one's 6-0 6-3 victory means she has dropped just 16 games in six matches so far.
Williams said: "It was a good match. Li Na's such a great player. It was tough at the end, I got a little nervous but I was able to close it out finally."
Williams and Azarenka played one of the best women's grand slam finals in years 12 months ago, with Williams edging it after Azarenka had served for the match.
The Belarusian, meanwhile, will take confidence from her two victories over Williams this season, including in Cincinnati last month.
"We always have really good matches," said Williams. "It's great to get to another final. She's a great player and she lifts her game whenever it counts. I think that's what makes the difference."
Williams had won her previous seven matches against Li but they had all been tight and the Chinesewoman had looked very good this tournament.
It was a surprise, therefore, that Li failed to win a single game in the opening set.
The fifth seed was spraying the ball all over the place, particularly with her forehand, while Williams was rock solid.
Remarkably, it was the world number one's third straight 6-0 set after she denied Carla Suarez Navarro even a game in the quarter-finals.
Williams won a 24th straight game at the tournament to open the second set but Li stopped the rot in the eighth game and then broke the American's fearsome serve to move ahead.
The US Open has been short on great matches and the crowd, who were desperate to see a real contest, responded.
Li is one of the few players who can live with Williams for power and athleticism from the baseline, but she blew a 40-0 lead in the next game and was pegged back to 2-2.
It was a big moment, and from there Williams moved up another gear.
Li battled to at least force her opponent to serve out the victory, saving six match points.
It was a slight glimmer of hope but Williams was in no mood to give her opponent any second chances and took her seventh match point to clinch victory after an hour and 27 minutes.
Earlier, second seed Azarenka defeated Italian Flavia Pennetta 6-4 6-2.
Two-time Australian Open champion Azarenka was just too strong for first-time grand slam semi-finalist Pennetta.
It was a competitive match in which both players struggled on serve.
Out of 18 games, 13 were breaks, with Pennetta holding her serve just once in the whole match.
The end of the first set was the key to Azarenka's victory.
The second seed let out a piercing scream after missing a simple volley at 30-30 in the ninth game but Pennetta was unable to capitalise and Azarenka eventually held to take the set.
Pennetta saved five set points but on the sixth Azarenka, somewhat ironically, came up with an unreturnable serve.
The second set was more one-sided and Azarenka clinched victory on her third match point with a forehand winner, although she surely must serve better in the final to stand a chance.
For Pennetta, it has been an outstanding tournament at the end of one of the most difficult years of her career.
The 31-year-old Italian missed the tournament last year after having wrist surgery that kept her out for six months, and she struggled on her return to the tour, dropping well outside the top 100.
Pennetta's results mean she will rise from her current ranking of 83 close to the top 30 when the standings are updated on Monday.
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