Asian champion Akhmadaliev was a silver medallist at the 2015 World Championships in Qatar's capital Doha and took a bronze at last year's Olympic Games in Rio de Janiero.

But much to his disappointment, he will be leaving Hamburg empty-handed after falling to a 4-1 loss to the unseeded Yeraliyev.

Awaiting the 2013 world bronze medallist in the quarter-finals is Germany’s Omar El-Hag, who delighted the home crowd with a split-decision win over Japan’s Ryomei Tanaka.

Among the other big names to fall short today were light welterweights Lorenzo Sotomayor of Azerbaijan and Vitaly Dunaytsev of Russia.

Sotomayor, the Rio 2016 silver medallist and top seed here, was beaten 3-2 by Egypt’s Eslam Mohamed.

It came just before Dunaytsev, the reigning world champion and Rio 2016 bronze medallist, had lost 4-1 to the United States’ Freudis Rojas.

Mohamed and Rojas will go onto face each other in the quarter-finals on Tuesday (August 29).

In contrast to Dunaytsev, there were victories for the three other defending champions that competed today.

Cuba’s Joahnys Argilagos begun his quest to retain the light flyweight crown with a hard-fought split-decision win over Puerto Rico’s Oscar Collazo.

Compatriot Arlen López showed why he is the reigning Olympic and world middleweight champion with a unanimous points victory at the expense of Italy's Salvatore Cavallaro.

Russia’s Evgeny Tishchenko, meanwhile, defeated Colombia's Deivis Julio Blanco 4-1 as the Rio 2016 Olympic gold medallist started his bid for a second consecutive world heavyweight title.

A unbeaten day for Cuba was completed following unanimous points wins for light welterweight Andy Cruz Gomez and heavyweight Erislandy Savón.

Cruz Gomez proved too strong for Ireland’s Sean McComb, while Savón cruised to victory over Ukraine’s Ramazan Muslimov.

Action in Hamburg is due to continue tomorrow with the second day of preliminary round matches in the flyweight, lightweight, welterweight, light heavyweight and super heavyweight categories.