Holidaymakers flocked to the region's beaches and tourist spots as temperatures touched 17C (62F).
However, forecasters said the clear, sunny weather would only last until today when a band of heavy rain sweeps across the region, sending the mercury plummeting.
Early risers in Cornwall may catch the last of the Bank Holiday sunshine in the morning, the Met Office said, while the downpour may not hit Devon until mid afternoon.
The start of the three-day festivities were tinged with tragedy after an elderly man and a young woman died on the region's roads.
A 72-year-old man on holiday in West Cornwall died on Saturday after being hit by a car while crossing the road outside Penzance the previous evening.
He was in collision with a silver VW Golf near the Trevellion farm shop on the A394 Marazion to Rosudgeon road, which was closed from 4.30pm until 10pm as investigators examined the scene.
In a bizarre and horrific incident in the early hours of Saturday morning mother-of-five Zoe Rhiannon Aspland, 30, from Yeovil, Somerset, was killed driving her Ford Ka the wrong way up the M5 motorway.
She died after her vehicle collided with four vehicles on the motorway in Somerset. It emerged yesterday that the unnamed woman had been naked while driving in wrong direction on the southbound carriageway from Weston-super-Mare.
Her car hit two vehicles before it was left stationary on the carriageway, where it was hit twice more.
An emergency worker said: "She was naked. And she was thrown out of the car by the impact.
"The police are trying to find out why she was in that state and what led her to drive the wrong way down the motorway."
Her parents Stephen and Karen Aspland paid tribute to their daughter. "Zoe was a loving mother to her five children and will be sorely missed by her brother Lee and sisters Alice and Laura," they said. "As a family we would appeal for privacy as we grieve for the loss of Zoe and ask any witnesses to the incident to come forward."
The road was closed while the emergency services dealt with the incident and it was reopened again at 7.30am.
Later that day a Coastguard team climbed down a 45ft-high cliff face to rescue a man who had become trapped on a ledge 25ft above the sea.
Police were alerted shortly after 1.35pm on Saturday that a person was trapped on a cliff edge somewhere in Torquay and immediately alerted Brixham Coastguard, launching a joint operation.
The force helicopter spotted the man at Corbyn Head, near the town centre, and an operation by the Coastguard rescue team brought him to safety.
A Coastguard spokesman said: "One of the team went down the cliff, secured the man then brought him back up."
In North Devon, a search and rescue helicopter from RAF Chivenor was scrambled after a boat full of passengers hit a rock at Skomer Island, off the Pembrokeshire coast. The Lady Helen sent out a mayday call just before 1pm saying it had run aground on the Welsh island and was taking on water.
Milford Haven coastguard launched a massive rescue operation including local lifeboats, a police boat and an RAF Sea King from the base at Chivenor.
Firefighters were also busy on Saturday when eight crews were called to deal with a blaze at a thatched house in Devon. A man was taken to hospital to be "checked over" as a precaution after fire broke out at the property in Bratton Clovelly, near Okehampton at about 5.45pm.