Li Na looked like a Grand Slam champion, while Laura Robson looked like a promising teenager.
The fifth-seeded Li avenged her third-round upset loss to the young Brit at last year's U.S. Open, winning in straight sets Friday at the same stage at Flushing Meadows.
Li, the 2011 French Open champ, rallied from down a break in the second set for a 6-2, 7-5 victory.
Li was nervous after she noticed that her draw was a repeat from last year. A pep talk from coach Carlos Rodriguez eased her anxiety.
"After the talk I was feeling much, much better," she said. "Because before I never try to share the feeling with the team."
Agnieszka Radwanska needed nearly two hours to slip past No. 32-seeded Anastasia Pavlyuchenkova 6-4, 7-6 (1). The third-seeded Pole faced 10 break points, but Pavlyuchenkova was able to convert only two, while Radwanska was 3 for 5.
A year ago, Robson's upset of Li was the biggest victory of her breakthrough run. Meanwhile, it was the third straight frustrating U.S. Open loss for the Chinese star.
Robson was ranked 89th coming into last year's tournament. She had never advanced past the second round at a Grand Slam event or defeated a top-10 opponent.
That all changed when she upset major champions Kim Clijsters and Li back-to-back to make the fourth round. Now 19, Robson was seeded 30th at Flushing Meadows and coming off a fourth-round run at Wimbledon.
Li had 34 unforced errors in their match a year ago, and she lamented then that the free points lifted the teen's confidence. This time, Robson never had much of an opening.
"She served very well today and I thought she was returning really deep," Robson said. "You know, there wasn't a lot I could do in some points."
Li surprised herself with 11 aces Friday — including one on a second serve on match point — and won all nine points when she went to the net. She's back in the fourth round at the U.S. Open for the first time since 2009.
Her run over, Robson now must face an unfortunate reality for many teenagers: getting her wisdom teeth out.
"All the other girls in the locker room are telling me their horror stories: 'Oh, yeah, I pulled my gauze out and it was just blood,'" Robson said. "So that's not too nice."
Sloane Stephens reached the fourth round for the first time, and a matchup against defending champion Serena Williams could be next.
The 15th-seeded Stephens beat 23rd-seeded Jamie Hampton 6-1, 6-3 Friday in the first match at Arthur Ashe Stadium between two American women younger than 24 since the Williams sisters met in the 2002 final.
Stephens has reached at least the fourth round at all four Grand Slam tournaments this season, including a semifinal run at the Australian Open in January, when she upset Serena Williams in the quarterfinals. That's one of only four losses for the top-ranked Williams in 2013.
Stephens lost in the third round at Flushing Meadows each of the last two years, beaten by 2008 French Open champion Ana Ivanovic both times.
Serena Williams will be back on court later Friday a day after playing singles and doubles, facing Yaroslava Shvedova in the nightcap at Arthur Ashe Stadium.
