Andrew Selby has admitted to feeling sluggish in his first Olympic win over Kazakhstan's Ilyas Suleimanov.
The Welshman battled to a 19-15 victory in his flyweight scrap, booking a quarter-final bout with Cuba's Robeisy Ramirez.
"I didn't feel at my best tonight and I was sloppy, but as the competition progresses I will get better," said Selby. "I just had to hit and move to win. The referee thought I was holding behind the head and grabbing, but it was him.
"I can and will box out of my skin from now on.
"I am buzzing now, especially as my mum was in the crowd. It was only the second time she has seen me box. She usually comes to the fights, but goes outside when it is my turn."
Selby won gold at the 2011 European Amateur Championships in Anakara.