A former city council leader said Labour has to reflect on the results after losing control to the Conservatives.
Christopher Hammond said the results for Southampton City Council came "as a bit of a surprise" on Saturday.
The Conservatives gained seven seats to sweep back to power after nine years.
Mr Hammond, Labour leader in the city, said his party "needs to change and adapt", the Local Democracy Reporting Service reported.
He said: "National circumstances did have an impact on us here in the city. The vaccine bounce has helped the Conservatives.
"People have been unclear nationally about what Labour is putting forward. We need to do more, sharpen up our messages and listen. Keir [Starmer] said that Labour needs to change and adapt."
He said Labour must reflect on the results and understand why the party's messages "do not resonate" with residents.
Pledging to hold the Conservative-led council to account for their promises, he said: "They are inheriting a rejuvenated council and they have got an incredible plan on the table."
Dan Fitzhenry, the leader of the Conservatives in the city, said his priority will be delivering on the manifesto's pledges.
After the announcement of the final results on Saturday, he listed a number of measures they will look to put in place "immediately", including freezing council tax in their first year in office, beginning work to create 1,000 parking spaces across council estates and tackling fly-tipping.
Among the Tories' pledges there are also plans to scrap evening parking charges in the city centre.
Mr Fitzhenry said: "Our priority for this year is about getting Southampton moving, recovering from this pandemic."