In the 2018 mayoral election for Makassar, Indonesia, Munafri Arifuddin was the only candidate, won a quarter of a million votes, and lost.

Makassar is the fifth-largest city in Indonesia, with a population roughly the size of Auckland, New Zealand, or San Diego, USA (just the city, not the urban or metropolitan area). So, as you can imagine, the mayoralty of such a city is hotly contested.
In 2018, it looked like Munafri Arifuddin was a lock to win the election and become the mayor of Makassar. For one, he had the connections: his uncle was the reigning Vice President of Indonesia. For another, he had the support: 43 of the city council’s 50 seats were held by political parties that backed his own (the Golkar Party). For another, he had the money and the popularity: Arifuddin was in charge of Makassar’s professional football club. And, finally, he had a unique edge: he was the only candidate on the ballot.
The city’s mayor prior to that election, Mohammad Ramdhan Pomanto, tried to stand against Arifuddin. However, the local electoral commission disqualified Pomanto on a technicality (apparently he had given away some cellphones?), leaving Arifuddin without a competitor. Only one thing stood in Arifuddin’s way: he still had to win a plurality of the vote.
Arifuddin received 259,955 votes, nearly 47% of the votes cast. But the other 53%? They were blank, “none of the above” votes. The supporters of Pomanto had encouraged empty ballots as a way of protesting his disqualification, and those empty ballots outnumbered Arifuddin votes by more than 37,000. According to electoral law, Arifuddin had lost the election.
Following this astonishing upset, legal appeals flew around trying to nullify the “none of the above” vote… but to no avail. Arifuddin and Pomanto faced off in the 2020 election, and Pomanto won back the mayoralty with 41% of the votes.