The 23-year-old was outstanding in the encounter, helping the Vicarage Road outfit win possession and capping it with a late goal as the Hornets reached the fifth round of the competition with a 2-0 victory over their Premier League counterpart.
The Spanish tactician who is pleased with the work-rate of the striker is delighted that the former Granada player crowned his effort with a goal.
“He [Success] scored at the end of the game, but he worked a lot during the game, fighting with all the defenders and trying to give different attacking options,” Gracia told club website.
“I think the goal was the reward he deserved.”
Success has now scored three goals in four games in the League Cup and FA Cup.
With only 12 starts in 26 appearances in all competitions, he will hope to get a starting role when Watford take on Tottenham Hotspur in their next Premier League game on Wednesday.