Indian opposition parties and political commentators cheered the election victory of a regional leader over Prime Minister Narendra Modi's ruling party in a big battleground state as a sign his populist sway could be checked.

Sunday's defeat came as Modi is being slammed publicly for failing to tackle India's explosive spike in coronavirus infections that has left the country in deep crisis, with hospital and crematoriums swamped and people dying for lack of oxygen.

Modi addressed dozens of...