Nadal, who won the Monte Carlo Masters for a 10th time last week, romped to the title without dropping a set on the newly renamed Rafa Nadal court at the Real Tennis Club in Barcelona, and needed just 90 minutes to finish off Thiem.
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Thiem had beaten the 14-times Grand Slam champion on clay in the Argentina Open last year and earned a place in the final by beating world number one Andy Murray for the first time in his career on Saturday, but he proved no match for Nadal.
The Mallorcan took a while to impose himself on Thiem on an overcast day in Barcelona with the cold weather slowing down the court.
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Thiem earned the first breakpoint of the match but Nadal recovered and eventually took the first set by breaking his opponent in the 10th game.
There was no let-up in the second set from Nadal, who broke the 23-year-old Austrian twice in a row before serving for the championship.
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