Hwang came on as a substitute just past the hour mark after logging minutes with South Korea in World Cup qualifying this week.
Watford threatened just before halftime when Ismaila Sarr sent a low pass across the face of goal to the arriving Josh King, who was unable to get a touch.
From a Wolves corner, Sierralta headed the ball into his own net. The Chile international’s status for the game had been in doubt after he missed international duty this week, with his country asking for the defender to be banned from playing this weekend.
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