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In contrast to her roller-coaster two previous matches, which both went to three sets, the 2011 French Open champion took just 55 minutes to get past her fourth round opponent.
In reaching the last eight, Li has matched her Wimbledon best, having made the quarter-finals in 2006 and 2010.
The 31-year-old will face either Polish fourth seed Agnieszka Radwanska or Bulgarian world number 72 Tsvetana Pironkova on Tuesday for a place in the semi-finals.
Li said she had been practicing returning slices with Jiang Shan, her husband and hitting partner, with her coach Carlos Rodriguez -- who mentored former world number one Justine Henin -- taking it all in.
"I was so nervous really because in the warm-up, my husband, he tried to hit slice. It's totally different men and women. I was feeling so bad," Li said.
"Before I came to the court, Carlos was talking to me because he already saw what happened. I was like, 'I can't catch the ball, he was hitting so much slice, I couldn't catch it at the right time'. But I think he was happy.
"For his job, he makes me unhappy; I think it's his job. I thought the match would be so tough because I know how good she will slice on the grass court."
Li beat Czech 32nd seed Klara Zakopalova 4-6, 6-0, 8-6 on Saturday after nearly blowing it in the final set, having beaten Romania's in-form Simona Halep with a similarly roller-coaster performance in the previous round, winning 6-2, 1-6, 6-0.
"I was surprised how was I hitting on the court," said Li.
"It was totally different from the last match. The last match I was feeling like it's not terrible, but I was feeling so tired.
"I was ready for running for another three hours again."
Li hit 26 winners to Vinci's eight, and her serving was far more reliable than the Italian's on the 2,000-seater Court 3.
Vinci, on a career-high world ranking of 11 matched her previous Wimbledon best in making the last 16, which she achieved last year.
However, the 30-year-old went into the match having never beaten Li in their previous three encounters, dating back to 2001.
Li's run to the Australian Open final earlier this year was the only other time she has made a Grand Slam quarter-final in nine majors since winning the French Open two years ago.
Results from the seventh day of Wimbledon (x denotes seeded player):Men's singles:
Fourth round:
Novak Djokovic (SRB x1) bt Tommy Haas (GER x13) 6-1, 6-4, 7-6 (7/4)
Tomas Berdych (CZE x7) bt Bernard Tomic (AUS) 7-6 (7/4), 6-7 (5/7), 6-4, 6-4
David Ferrer (ESP x4) bt Ivan Dodig (CRO) 6-7 (3/7), 7-6 (8/6), 6-1, 6-1
Juan Martn Del Potro (ARG x8) bt Andreas Seppi (ITA x23) 6-4, 7-6 (7/2), 6-3
Lukasz Kubot (POL) bt Adrian Mannarino (FRA) 4-6, 6-3, 3-6, 6-3, 6-4
Jerzy Janowicz (POL x24) bt Jurgen Melzer (AUT) 3-6, 7-6 (7/1), 6-4, 4-6, 6-4
Fernando Verdasco (ESP) bt Kenny De Schepper (FRA) 6-4, 6-4, 6-4
Andy Murray (GBR x2) bt Mikhail Youzhny (RUS x20) 6-4, 7-6 (7/5), 6-1
Women's singles:
Fourth round:
Sabine Lisicki (GER x23) bt Serena Williams (USA x1) 6-2, 1-6, 6-4
Kaia Kanepi (EST) bt Laura Robson (GBR) 7-6 (8/6), 7-5
Agnieszka Radwanska (POL x4) bt Tsvetana Pironkova (BUL) 4-6, 6-3, 6-3
Li Na (CHN x6) bt Roberta Vinci (ITA x11) 6-2, 6-0
Sloane Stephens (USA x17) bt Monica Puig (PUR) 4-6, 7-5, 6-1
Marion Bartoli (FRA x15) bt Karin Knapp (ITA) 6-2, 6-3
Petra Kvitova (CZE x8) bt Carla Surez (ESP x19) 7-6 (7/5), 6-3
Kirsten Flipkens (BEL x20) bt Flavia Pennetta (ITA) 7-6 (7/2), 6-3
