It was the world number one's first match since losing in straight sets to Novak Djokovic in the final of the World Tour Finals in London on November 11.
Playing ahead of the official ATP season-opener in nearby Doha next week, Ferrer looked the sharper from the start, breaking in the ninth game to take the first set.
It was more of the same in the second set as Nadal struggled to find his range against an opponent who already had a game under his belt, having defeated Stanislas Wawrinka in the quarter-finals on Thursday.
"I am happy with the state of my game and will look to produce my best tennis for the final."
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In the second semi-final world number two Djokovic defeated Jo-Wilfried Tsonga of France 7-6 (7/5), 6-3 under the watchful eyes of new coach Boris Becker.
In earlier action, Andy Murray chalked up his first win since returning to action after a three-month injury lay-off by defeating Switzerland's Wawrinka 6-3, 6-4.