For two months, Ocean Network Express had that honour, being possession of the 20,150-TEU MOL Triumph, noted London's Loadstar.
The ship was named at a ceremony at Samsung Heavy Industries in Geoje, South Korea.
'This is a very exciting time for all of us because today marks the first time that OOCL is receiving newbuildings in the 21,000-TEU size,' said OOIL chairman CC Tung.
'In fact, the OOCL Hong Kong will be a titan among containerships at sea, with a carrying capacity at 21,413 TEU. An important milestone for us at OOCL indeed,' he said.
The vessel is the first of six identical ships ordered by OOCL at SHI in April 2015 for a total cost of US$950 million.
The christening of OOCL Hong Kong comes less than two months after the 20,150-TEU MOL Triumph made headlines as the first ship to surpass 20,000 TEU, but its reign as the 'largest ship' was short when the 20,568-TEU Madrid Maersk appeared in April.
Said Mr Tung: 'Faced with increasing competition and un-ending pressure on costs, we need to take the bold step in operating larger size ships of quality and high efficiency in order to stay relevant and compete effectively as a major container shipping company.'
The OOCL Hong Kong will be serving the Asia-Europe trade lane on the LL1 service with stops in Shanghai, Ningbo, Xiamen, Yantian, and Singapore, and via Suez Canal to Felixstowe, Rotterdam, Gdansk, and Wilhelmshaven, before making its return leg.