Alcaraz wins in 56 minutes as 'China's Nadal' extends Beijing fairytale
Rain in Beijing played havoc with the schedule but four-time Grand Slam champion Alcaraz made rapid progress under the roof of the Diamond Court with a 6-1, 6-2 demolition of Tallon Griekspoor.
The 39th-ranked Dutchman looked shellshocked.
Alcaraz, the second seed behind Jannik Sinner, faces seventh-seeded Karen Khachanov next after an ominous showing of intent from the 21-year-old Spaniard.
The Russian Khachanov booked his place with a hard-fought 7-6(4), 7-6(9) victory over Argentina's Francisco Cerundolo.
In the only other match completed on the day in the men's draw, Chinese wildcard Bu Yunchaokete pulled off a shock 6-2, 6-4 win over Italian sixth seed Lorenzo Musetti.
There was home joy too in the women's draw as another Chinese wildcard, Zhang Shuai, reached the last 16 to add another chapter to her fairytale tournament.
The 35-year-old had not won a singles match in more than 600 days when she arrived at the prestigious WTA 1000 event last week.
The two-time Grand Slam singles quarter-finalist, who has been plagued by injuries, has now won three matches in a row after a 6-2, 6-3 defeat of Belgium's Greet Minnen.
Zhang, who faced Minnen as the lowest-ranked player to reach the China Open third round in the tournament's history, faces Poland's 23rd seed Magdalena Frech next.
Zhang hails from Tianjin, near Beijing, and said she felt very much at home on the hard courts of the Chinese capital.
So at home in fact that she compared herself jokingly to the Spanish great Rafael Nadal on his favourite surface of the French Open.
"When I am on the court I feel so like Rafa Nadal on Court Philippe-Chatrier," she laughed.
US Open runner-up Jessica Pegula survived a scare to set up a meeting with Spain's Paula Badosa.
The second seed from the United States fought back to beat Russia's Veronika Kudermetova 6-7(9), 6-1, 6-2.
The 30-year-old Pegula is chasing a seventh WTA Tour title.
The 19th-ranked Badosa booked her place with a straight-sets win over Slovakian qualifier Rebecca Sramkova.
The top women's seed in Beijing is Aryna Sabalenka, who defeated Pegula in New York earlier this month for her third Grand Slam crown.
World number one Iga Swiatek is not in Beijing because of "personal matters".