Vandals who sliced through TV cables to leave 100,000 viewers without pictures of England's World Cup clash with Ecuador were "experts", the firm says.
Telewest subscribers in Bristol, Bath and the Cotswolds missed the match after the blackout on Sunday afternoon.
The fault occurred when two major underground cables in the Stone and Patchway areas of Bristol were cut.
The company says those responsible "knew what they were doing" and had gone to great lengths to cause trouble.
"These cables are underground and extremely secure," said Telewest spokesman John Moorwood. "It wasn't kids messing around - the way they were cut was fairly strategic.
"We normally have a back-up system, but the nature of the cuts meant that it led to a major fault."
The firm, which merged with NTL earlier this year, said it would discuss compensation on a case-by-case basis.
NTL spokeswoman Alexandra Legg said repairs were made as quickly as possible.
"We would like to say a huge apology to anyone who was hoping to watch the match," she said.
"It couldn't have happened at a much worse time - an hour before one of the biggest games ever."
One viewer said: "Panic set in as people jumped in their cars to find a place to watch the match.
"The Telewest helpline went down as well, no doubt due to the thousands of callers."
Callers to BBC Radio Gloucestershire said they went to neighbours' houses or the local pub to watch the match.
Services to about half the customers were restored by about 0400 BST on Monday. All were expected to be reconnected by 1300 BST.
NTL has called in police to investigate who damaged the two buried cables.