A glint of violence more common around stop-and-gos in the city's rough neighborhoods struck a busy Starbucks in South Philadelphia, where on Saturday, for no apparent reason, a man repeatedly stabbed a patron waiting for his order, including once in the face.

Police said the 5:44 p.m. assault, which left the 29-year-old victim in critical condition yesterday at the Hospital of the University of Pennsylvania, remained under investigation. It was unclear whether the attack stemmed from an argument or was just an outburst by a deranged person.

Based on eyewitness accounts, however, police arrested a suspect around 8 a.m. yesterday at the same Starbucks, at 2201 S. Broad St., between Jackson and Wolf Streets.

Detectives said the man, a Philadelphia resident, was "known to police" from previous contact with law enforcement but declined to elaborate. The man was being questioned last night.

Although the coffeehouse is adjacent to the Methodist Division of Thomas Jefferson University Hospital, the victim was rushed to HUP's trauma unit in West Philadelphia "because of the seriousness of his injuries," said Lt. David Bellamy of the South Detectives Bureau, which is investigating.

A manager at the shop referred questions to Starbucks' corporate headquarters in Seattle, which was closed for the weekend.

Although the violence seemed out of place amid the aroma of ground cinnamon and baristas serving premium blends, it was not a total surprise for the neighborhood, said Lt. John Newman, a Jefferson Hospital security guard, who noted that the bank that shares the parking lot with Starbucks had been the target of frequent robbery attempts.

Contact staff writer Michael Matza at 215-854-2541, or mmatza@phillynews.com.