The Brazilian defender curled an unstoppable shot past Pepe Reina as United ran out 2-1 winners at the home of their bitter rivals.
His effort garnered 50 per cent of the votes cast by Eurosport-Yahoo! readers.
In second place was Steven Gerrard for his accomplished finish in the same game.
Poll results - who scored the best Premier League goal of last weekend?
1. Rafael (Manchester United v Liverpool) - 50%
2. Steven Gerrard (Liverpool v Manchester United) - 31%
3. Ashley Cole (Chelsea v Stoke) - 11%4
4. Nathaniel Clyne (Southampton v Aston Villa) - 3%
5. Steven Fletcher (Sunderland v West Ham) - 2%