Rosie Eccles admitted she was "heartbroken" after losing her opening bout in the Boxing Road to Tokyo Olympic qualifying event at the Copper Box Arena on Sunday.
Eccles lost a split points decision to Russian fourth seed Saadat Dalgatova and the Welsh welterweight told Boxing News: "I don't know what to say to be honest with you, I'm absolutely heartbroken.
"I knew what to do to combat her style, but one way or another, according to the judges, I didn't do that.
"It wasn't a nice fight to be in, it was just messy. I pride myself on getting my tactics right but maybe I was a little too eager against someone who wants to get in there and tie you up."
Irish light-heavyweight Emmet Brennan made an excellent start to his campaign by stopping Bosnia's Radenko Tomic inside two rounds, while lightweight George Bates also advanced when Spanish opponent Leon Dominguez Becerra was halted by a cut.
Welterweight Christina Desmond lost a unanimous decision to Italy's Angela Carini.