Newhaven and Eastbourne lifeboats and the Coastguard helicopter launched at 8.50pm.
The Newhaven crew found the sailor at 9pm, drifting towards the rocks under Seaford Head.
Amid strong winds and breaking waves, one crew member managed to board the sailing boat.
But a second crew member was swept overboard and had to be pulled from the sea.
At 9.15pm the helicopter winched a paramedic onto one of the lifeboats.
The crew member on board the sailing boat assessed the casualty and steered back towards Newhaven harbour.