LUSAKA, Aug 16 (Reuters) - Zambian President Edgar Lungu conceded defeat on Monday, after a landslide election win by opposition leader Hakainde Hichilema, who will face the challenge of reviving an economy in turmoil. With all but one constituency counted, Hichilema had won 2,810,777 votes against Lungu"s 1,814,201, and the electoral commission declared him president. It marked the country"s third peaceful handover of power to an opposition party. "I will comply with the constitutional provisions for a peaceful transition of power. I would therefore like to congratulate my brother, the president-elect, His Excellency Mr Hakainde Hichilema," Lungu, 64, said in a short televised address to the nation. When the celebrations die down, Hichilema, 59, a former CEO at an accounting firm before entering politics, will need to focus on resuscitating a flagging economy. Zambia became Africa"s first pandemic-era sovereign default in November after failing to keep up with its international debt payments. read more "It is in no doubt what the instruction is to all of us (that you) ... elect us to office at a very difficult time," he said, hinting at the task ahead as he addressed supporters in the capital, Lusaka "We will not let you down." The default was driven by depressed commodity prices - which had pushed Zambia into recession well before the COVID-19 pandemic - worsened by the pandemic itself. URGES UNITY He has some room for manoeuvre as the economy has been buoyed slightly by more favourable copper prices this year - now hovering around decade highs, driven partly by the boom in electric cars. Last year, Zambia, Africa"s second biggest copper miner, produced a record output of the metal. Nonetheless Hichilema urged Zambians to put aside divisions, condemning attacks on property, after a mall named after the ex-incumbent was looted. "For years we were victims of retribution. We are not about to .... start a new wave of violence," he said. "If you want to show higher moral ground ... do not attack them." The election is the culmination of an acrimonious rivalry between the two that in 2017 led Lungu to arrest and imprison Hichilema for refusing to make way for his motorcade. This is Hichilema"s sixth attempt at the presidency since 2006. He touted his nationwide success, even in perceived Lungu strongholds, as evidence that Zambia had dodged ethnic division. "Victory ... (has) been delivered by all the 10 provinces of Zambia ... isn"t that lovely?" he said, to applause. Lungu had cried foul on Saturday, calling the election "not free and fair" after violence against ruling Patriotic Front party agents in three provinces, but the size of the margin made it near-impossible to challenge the result in court. Power has switched from a ruling party to the opposition twice before since independence from Britain in 1964. The latest shift strengthens Zambia"s democratic credentials and sets an example on a continent with a patchy history of peaceful change. Wearing the red and yellow of Hichilema"s United Party for National Development (UPND) Hichilema"s supporters celebrated, dancing and singing, while drivers honked their horns. "This victory is so sweet," 37-year-old Jane Phiri said, next to her market stall. "This spirit of change was bottled up for a long time." Zambia"s sovereign dollar bonds jumped nearly 2 cents on Monday after the news of Hichilema"s win. read more Zambia"s kwacha currency strengthened nearly 1% against the dollar. International Monetary Fund support is on hold until after the vote, as is debt restructuring - seen as an early test for a new global plan aimed at easing poor countries" burdens. read more Reporting by Chris Mfula; Additional reporting by Karin Strohecker and Tom Arnold in London; Writing by Tim Cocks; Editing by Catherine Evans and Alison Williams Our Standards: The Thomson Reuters Trust Principles.