Electricity is pulsing through Spain and Portugal again after a massive outage knocked out power in both countries on Monday. So too are questions.

MADRID (AP) — The cause of Spain and Portugal’s widespread blackouts remained a mystery on Tuesday, with some isolated disruption remaining after power was largely restored to both countries.

Electricity was back in most of the two countries almost 18 hours after a blackout that shut down much of daily life. The cause of the outage remained unclear.

Play was suspended at the Madrid Open the afternoon of April 28 before being canceled for the day and night, due to a power outage across Spain and the Iberian Peninsula. The loss of power meant that the electronic line calling (ELC) system used to judge whether a shot has landed in or out did not work,

Play at the Madrid Open tennis tournament has been suspended because of a major power outage reported in Spain and Portugal.

A major power outage reported in Spain and Portugal has shut down matches, including the one between Britain's Jacob Fearnley and Grigor Dimitrov, at the Madrid Open. Two singles matches and one doubles match were underway when the power went out.