The forward fired home from close range to seal the victory after Roberto Pereyra and Gerard Deulofeu had earlier given the Hornets, a two-goal lead.
The 22-year-old who has struggled to impress since his arrival at the Vicarage Road has thus ended his two-year wait for his second English topflight goal.
Delighted with the feat, the former Granada player has expressed his appreciation to his teammates and the fans for their support.
“I am happy for my first league goal of the season,” Success told club website.
“I am super proud. A big thank you to the team for supporting me. I am happy to be supporting this team.
“I just want to take my chance and make the team better. The fans have been brilliant since the start so thank you to them also. I really appreciate them.”
Success who has scored three goals in all competitions this season will be aiming to build on the performance in their next league game against Newcastle United on Saturday.