The Barbuda People's Movement, allied to the UPP, won one seat.
"[The result] may not have been the one that we would have preferred"
Baldwin Spencer, the prime minister
Speaking to supporters on Friday, Spencer admitted that the narrow result "may not have been the one that we would have preferred".
But on the UPP website, he wrote: "We are humbled to have received this mandate from you to keep our country moving on the right track and headed in the right direction."
The northeastern Caribbean nation, populated by 85,000 people, received an economic blow last month with the collapse of Allen Stanford's Houston-based financial empire.
The country has been struggling in recent weeks to deal with the fallout of US allegations that Stanford operated an $8bn Ponzi scheme through his Antiguan-based offshore bank.
The Texas billionaire was Antigua's largest investor and employer. His holdings included Stanford International Bank, the Bank of Antigua, cricket grounds, restaurants and other businesses as well as hundreds of hectares of land.
In 2006, the former British colony bestowed a knighthood on Stanford.
After the US securities and exchange commission filed fraud charges against Stanford, his senior executives and his companies, the Antigua and Barbuda government moved to seize his assets.
Antigua and Barbuda is one of the Caribbean's most prosperous nations, because of tourism and offshore financial services.
Relatively undeveloped Barbuda is home to smaller, more exclusive resorts.