The crew of the RNLI's Tower lifeboat beat the rising waters of the Thames to save an injured man at Woolwich on Monday.
He had suffered spinal injuries after falling 25ft from the river wall onto the exposed riverbed.
Rescuers launched from their base next to Waterloo Bridge at 6.44pm on following a 999 call for help to the Coastguard.
They arrived at the scene minutes later to find the man being treated by paramedics on the foreshore of the south side of the river, about 200m upriver from the Woolwich ferry terminal.
RNLI lifeboat helmsman Mick Neil said: "It appeared the two men were on a night out when one of them went over the handrail and fell onto the exposed river foreshore, injuring his spine.
"His friend then slid down the vertical river wall in an attempt to help him, suffering cuts, bruises and an injury to his ankle.
"From the start the rescue was time critical as the rising tide was rapidly covering the area of ground we were all on. Initially the water was at his ankles but it quickly got up to his knees."
Paramedics and the RNLI lifeboat crew placed the injured man onto a spinal board but were soon cut off by the rising waters.
Mick said: "As always with suspected spinal injuries you have to be very careful when moving someone. He was conscious throughout but in a lot of pain.
"Once he was secure we got him, his friend, the police and paramedics onto the lifeboat and took everyone to Woolwich Arsenal Pier where we were met by an ambulance."