The corridor between Courts 16 and 17 was cleared by police and Mattek-Sands, on a stretcher, was wheeled down to an ambulance by Gate Four at 5.10pm.
Chilling screams of "f**k, help me, help me" rang out around the famous Tennis venue.
The Romanian said: "I saw she was on the floor, then she started screaming".
"But, for me, I was there; it felt like so long".
"I freaked out. I have never seen such an injury before, the knee was really in a bad position. Fuck!" she can be heard saying on the video.
"She went into shock".
Mattek-Sands lives in Phoenix, Arizona with her husband Justin Sands and beloved mastiff dog Ruger. She was still screaming more than 15 minutes later, according to Ben Rothenberg of the New York Times.
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Cirstea appeared to question the time it took for treatment to arrive, prompting an All-England Club statement.
But they insisted the stretcher was on court well before it was needed, stressing the correct medical procedures are to provide painkillers and keep the player motionless while they are being assessed.
"The player was then transferred directly to an ambulance and taken under emergency conditions to a hospital".
A wild-card entry to the singles at Wimbledon, Mattek-Sands is a doubles specialist and in tandem with Lucie Safarova has won the last three grand slam titles, at the US Open, Australian Open and French Open.
After nearly 20 minutes of on-court medical attention, Mattek-Sands was stretchered away to receive more treatment. She was later seen in tears courtside.
On social media, users expressed horror and agreed with Cristea's assessment that medical personnel took too long to respond.
To the casual tennis fan, Mattek-Sands is nearly certainly best known for her dress sense.