Taking a break from the general-election campaign, the former prime minister who in 1984 signed the Hong Kong people over to Chinese rule was back to open the pounds 600m bridge which will link the territory's new island airport with the mainland.
Built in just five years, the main span of the bridge is 1,377m long - 97m longer than San Francisco's Golden Gate Bridge, making it the world's largest road and rail suspension bridge.
The total length of the two- section bridge is 2.14km.
Eyebrows were raised in Hong Kong when it became apparent that Lady Thatcher, rather than a Chinese or local official would open the bridge.
Yesterday's event was notable for the absence of Tung Chee-hwa, who will head the first post-colonial government. He had been invited to join the Governor, Chris Patten, on the platform but declined.
British officials constantly insist that they wish to avoid British triumphalism in Hong Kong. But the airport and associated projects are seen by China as partly designed for British aggrandisement.
This impression was hardly diminished by the arrival of four helicopters during the opening ceremony, with the lead aircraft trailing a giant Union flag.
British modesty was, however, manifest in a parade representing countries that had contributed to the building of the bridge.
Many countries were driving British-made vehicles - Belgium was represented by a Rolls-Royce, Japan by a double-decker bus - but a vehicle representing Britain itself was inexplicably absent. China was represented by a minibus.
Lady Thatcher spoke of the bridge providing a good example of co-operation. In reality, the start of the project was delayed by acrimonious Sino-British wrangling over who would pay for the project.
Once the go-ahead was given, the bridge was built both on time and within budget. "From my own experience in government," said Lady Thatcher, "I know that these things do not invariably turn out like that ... except in Hong Kong."
Security was tight for the spectacular opening ceremony, crowned by a pounds 400,000 fireworks display.
Some 2,500 police officers were deployed to control the massive crowds which turned up for the fireworks display, and also because the authorities feared that Lady Thatcher might be a target for an IRA attack.
Protesters, unhappy about Britain's lack of action over the establishment of a Chinese-organised rival legislature in Hong Kong, were kept well away from the opening ceremony.
Mr Patten said that Lady Thatcher's "commitment to Hong Kong and to the values that the people of Hong Kong hold dear is known and honoured." Yet Lady Thatcher remains a controversial figure in the colony.
China's supporters cannot forget her belligerent attitude towards China when negotiations over the return of Hong Kong began in 1982.
They were particularly angered by her suggestion that China wished to break its treaty obligations towards Hong Kong.
Hong Kong's democratic camp, by contrast, remembers Lady Thatcher as the prime minister who refused to listen to the view of local people over the deal she negotiated with China.
Lady Thatcher will be in Hong Kong for the handover ceremony on 30 June.
She has consistently shown more interest in the fate of Britain's last major colony than in many other foreign-policy issues.