The Chinese port moved more containers than Singapore did from April to last month, and may clinch the leader's status by year-end.
Last month's data from the Maritime and Port Authority of Singapore (MPA) showed that Shanghai moved 2.44 million TEU to Singapore's 2.39 million.
In six straight months, Singapore carried 14.05 million TEUs versus Shanghai's 13.85 million, equivalent to 200,000 container boxes more, or a difference of about 40 average-sized container ships.
A strong rebound in world trade this year has had container traffic through Shanghai's ports growing at a blistering pace of 19 percent over last year's figure, compared with Singapore's 14 percent.
Analysts had expected Shanghai to pip Singapore as early as two years ago, but that did not happen when the global recession put a dent in Chinese exports.
Although Singapore may lose the bragging rights that come with being number one, it should continue to benefit from its hub status; the maritime industry contributes seven per cent to its gross domestic product and employs more than 100,000 people.
Singapore surpassed Hong Kong as the port with the highest container traffic five years ago, and has held the unofficial title since then.