The second-seeded Nadal dominated 2003 title-winner Roddick for stretches, racing to a 4-0 lead thanks to two service breaks in the opening 18 minutes, then taking 16 of the last 17 points in the second set.
The 21st-seeded Roddick had both legs massaged by a trainer in the third set.
Seeking his 11th Grand Slam title, Nadal hasn’t dropped a set in the tournament.
In Saturday’s semifinals, he’ll face No. 4 Andy Murray who beat No. 28 John Isner earlier Friday.
Nadal owns a 12-4 lead against Murray, including victories in the semifinals at the French Open and Wimbledon this year.