The Spaniard completed the 45.5km course, which started and finished with gentle climbs as well as featuring constantly undulating terrain, in a time of 58 minutes 13 seconds, with Belgian champion Victor Campenaerts finishing 30 seconds in arrears to take the silver medal and Italy's Moreno Moser a further nine seconds back in third place.
2016 marked the first year the event was open to professional riders and, though the big names of Fabian Cancellara, Tony Martin, and Tom Dumoulin were absent, Castroviejo lined up as one of the big favourites after his second place behind Chris Froome in the 37km Vuelta a Espana time trial last week.
"Taking on such a TT just four days after a Vuelta a España is really difficult," Castroviejo said. "It all depends on how you have finished things off there, if your team did well and you've got morale - I really tried to recover as much as possible, eat much and healthy, have as much rest as possible, and keeping my mind focused on this tough course, almost an hour-long one, with rough roads, small climbs, plenty of elevation gain. Fortunately, things turned out well."
It was the 29-year-old's first win of a season that was cut short in February, when he crashed into a spectator while descending from the stage finish in the Volta ao Algarve and fractured his cervical vertebrate. He spent two months in a neck brace and four months out of competition.
It is also the Spaniard's first major victory after being twice Spanish time trial champion.
"Having such experience from so many close calls really helped me today. You know that in such demanding courses, an effort of 55-60 minutes, everything can be lost on the last few kilometers, and as we saw that the start also suggested to take on a big gear and push hard, I rather decided to save some energy and stay calm for the end. We knew the Côte de Cadoudal and it was more than necessary to save some legs for the end. That was the plan, we developed it, and we delivered - I'm so happy!"
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