"But if you add that he is playing very well now from the baseline, he is one of the toughest opponents you can meet".
Playing in his first tournament since his victory at last month's U.S. Open, Nadal rolled to a 6-3, 6-3 victory over Karen Khachanov of Russian Federation.
The first nine games of the second set went with serve, but Wozniacki faltered when serving for the first time to stay in the match.
The 31-year-old Nadal broke Khachanov, ranked 42 in the world, in the fourth game and was never in serious trouble after that.
Cirstea follows fellow Romanian Simona Halep into the quarter-finals after the second seed sent Maria Sharapova packing on Wednesday. Isner had eight aces and won 84 percent of his points on his first serve.
"I'm happy about the match today".
World number one Garbine Muguruza and reigning champion Agnieszka Radwanska are both out, leaving world number two Halep as the favourite in the Chinese capital.
Also into the quarter-finals are Caroline Garcia, who defeated French compatriot Alize Cornet 6-2, 6-1, and Czech Barbora Strycova, who beat Daria Gavrilova of Australia 6-0, 6-4. The Spaniard is coming off a big win in the US Open and he is full of confidence playing on the hard court like he will be in this game.
The American has so far beaten Malek aziri and Leonardo Mayer to reach the quarter-finals.