According to The New York Post, it was almost 20 minutes before medical staff were able to remove her from the court on a stretcher into a waiting ambulance.
Mattek-Sands was playing Romania's Sorana Cirstea on outside Court 17 when she appeared to slip as she approached the net at the beginning of the third set then collapsed awkwardly to the grass.
Safarova was inconsolable after the horrific injury to her doubles partner.
Chilling screams of "f**k, help me, help me" rang out around the famous Tennis venue. It's clear there was confusion from her opponent, staff and the crowd about the severity of the injury.More news: S & U PLC (LON:SUS) Now Covered by Peel Hunt
Mattek-Sands reportedly exclaimed, "Help me, help me", as she waited for paramedics to come to her aid.
Safarova was later seen arriving at the court in tears. "These painkillers are not working", she was heard to say before she was taken off the court, according to The Sun.
"I went over and saw her knee out and turned around and told them to bring a stretcher because I think everyone froze", she said.
She was eventually attended to by medical personnel.More news: Eastbourne 2017: Novak Djokovic eases into final by beating Daniil Medvedev
Speaking for the first time about the incident, Cirstea said: "I'm not a doctor, I'm not a specialist". In this kind of moment when she was screaming so loud, you watch the knee, it was a very uncomfortable moment.
The 32-year-old Mattek-Sands is ranked No 1 in women's doubles.
In a statement, the All-England Club said: "The first response to Court 17 was within one minute, by a qualified ambulance technician".
To the casual tennis fan, Mattek-Sands is nearly certainly best known for her dress sense. She was forced to retire from the second-round match and was taken to the hospital.More news: Wildfires spread throughout 5 states forces evacuation of thousands