72-hour free transit in Beijing although visiting China after Hong Kong?

In july I'll be flying from Ulaanbaatar to Beijng and i am planning to fly from Beijing to Hong Kong within 72-hours. After visiting Hong Kong I would like to enter mainland again by going to Guangzhou. I'll apply ahead for a single-entry visa for visiting Guangdong and surrounding regions. Is it still possible to make use of the 72-hour free transit in Beijing, although I would be having a single-entry for China which I want to use after visiting Hong Kong?