The 24-year-old, winner of the Olympic gold medal at Rio 2016, was beaten by virtue of a 3-2 split decision in favour of his unseeded opponent.

Amankul’s reward is a semi-final encounter with Azerbaijan’s Kamran Shakhsuvarly, who edged Colombia’s Jorge Vivas Palacios by the same scoreline.

The four other current world champions competing today all won, including three of López’s fellow Cubans.

Light flyweight Joahnys Argilagos beat Germany’s Salah Ibrahim Omar in the first bout of the day in Ring A, claiming a unanimous points win over the home favourite.

Awaiting him in the semi-finals is Kazakhstan’s Zhomart Yerzhan, a 5-0 winner at the expense of Russia’s Vasilii Egorov.

Cuba’s Lázaro Álvarez Estrada continued his bid for a third-straight world lightweight title with a 5-0 victory over Germany’s Murat Yildirim.

Compatriot and three-time reigning world light heavyweight champion Julio César La Cruz beat another home favourite, Ibragim Bazuev, by the same margin.

Álvarez Estrada’s next challenger is due to be Georgia’s Otar Eranosyan, who overcame fourth seed Elnur Abduraimov of Uzbekistan.

Standing between La Cruz and another final is Ecaudor’s Carlos Mina Caicedo following his unanimous points win over Tajikistan’s Shabbos Negmatulloev.

Also still on course for the defence of his world title is Russia’s Evgeny Tishchenko after the Olympic champion beat New Zealand’s David Nyika 4-1.

It was not without controversy, however, with Nyika taking to social media to question the five judges’ decision.

"Today I put on a clinic against reigning Olympic and world champion," the 22-year-old, aiming to become just the second New Zealander to win a medal at a World Championships, said on his Facebook page.

"I feel like I'm the punch line of some sick practical joke in this sport.

"Nevertheless I'm still here, and remain loyal to my craft."

Tishchenko beat Kazakhstan's Vassily Levit to the Olympic gold medal at Rio 2016, despite appearing to be on the back foot throughout.

It was one of several decisions believed to be suspect as boxing competitions at the Games received widespread criticism.

Tishchenko’s semi-final opponent here will be Uzbekistan’s Sanjar Tursunov, who defeated The Netherlands’ Roy Korving.

It was a disappointing day for Germany as the home nation suffered two more defeats on top of those at the hands of the Cubans.

Artem Harutyunyan was eliminated from the light welterweight competition after losing 3-2 to Uzbekistan’s Ikboljon Kholdarov.

It came after fellow German Omar El-Hag had tasted defeat in his bantamweight quarter-final with Kazakhstan’s Kairat Yeraliyev.

Germany’s only winner today was welterweight Abass Baraou with a 5-0 success over Mongolia’s Tuvshinbat Byamba.

Action in Hamburg is due to continue on Thursday (August 31) following a rest day tomorrow.

Taking centre stage will be the semi-finals in the light flyweight, bantamweight, light welterweight, middleweight and heavyweight categories.