Juan Martin del Potro stormed into round two with a 7-6 (4) 6-4 win over Uruguay's Pablo Cuevas and will face third seed Grigor Dimitrov, who battled past Bosnian Damir Dzumhur 6-1 3-6 6-3.
Elsewhere, top seed Marin Cilic cruised into the Japan Open semi-finals with a 6-2 6-0 win against Ryan Harrison.
"I think it was just a hair or something, a hair from the tennis ball".
Nadal is bidding to win this tournament for the sixth time but believes the rapidly improving Dimitrov, who beat Roberto Bautista-Agut in three sets to book his place in the last four, will represent a hard opponent.
Nadal told atpworldtour.com: "He is a player that I really like, a good friend on the tour. I think I did the things that I want to do, and I did it well, so very happy".
"The doctor suggested I get it treated, but I can only rest after the season, that's the plan", said Peng, ranked 25th in the world.
"He's a great guy".
Rafael Nadal and Grigor Dimitrov face off in what could be a scintillating semifinal encounter at the China Open as the Bulgarian looks to pull off the upset in their tenth meeting of their careers. Let's see. I going to try to play my best.
Kyrgios, 22, enjoyed an easy passage into the last four when Belgian qualifier Steve Darcis retired at 6-0 and 3-0 down to the Australian.
He is looking to go on and make the semi-finals for the second time.
To bump Garbine Muguruza from No. 1, the Romanian needs to reach the final.
Second seed Alexander Zverev served seven aces as he beat Britain's Kyle Edmund 6-3 7-6 (3) in the day's last match and will meet Italy's Fabio Fognini in the next round.
Halep and Ostapenko met at the French Open earlier this year, with the Latvian winning the duel.
Kvitova said with the end of the season in sight, many players are running on empty. "That time was for him, today was for me".