Rights-holders to Saturday's Mayweather v Pacquiao boxing match have forced recordings of the bout to be removed from the video streaming app Periscope.
But TV networks HBO and Showtime would have been too late to prevent some users from watching the action live.
The firms had charged the public a record $89.95 (£59.50) to watch the fight in standard definition and an additional $10 in high definition.
They both declined to comment on the misuse of the Twitter-owned app.
However, HBO has previously expressed its displeasure following reports of Periscope being used to rebroadcast the opening episode of the latest series of Game of Thrones.
"In general, we feel developers should have tools which proactively prevent mass copyright infringement from occurring on their apps and not be solely reliant upon notifications," it said at the time.
'The winner is...'
More than one million people have joined Periscope, which launched on 26 March.
Users sometimes use it to "pirate" copyright-protected footage by filming their TV screens with their smartphone cameras.
The resulting footage is often poor quality, but sufficient to follow what is going on.
Unlike other live streaming services - including YouTube and UStream - Periscope does not provide tools to let content owners force the removal of copyright-infringing content in near-real time.
Instead, it requires that they file individual takedown requests, which take longer to process.
Twitter's chief executive, Dick Costolo, was criticised by some users of his social network after he tweeted: "And the winner is... @periscopeco" on the night of the Las Vegas fight.
"Guess pirating copyrighted content is Twitter's new business model," responded one user.
However, Mr Costolo was likely referring to the fact that HBO itself had promoted the app earlier in the evening when the broadcaster used it to stream footage from Manny Pacquiao's dressing room.
"Broadcasting content that is protected by copyright is a clear violation of our content policy," said a spokeswoman for Twitter.
"We received 66 reports from rights-holders and took action against 30 broadcasts in response to the reports. The remaining broadcasts had already ended and were no longer available. We were able to respond within minutes."
Some people also used the rival live-streaming app Meerkat to stream the fight.
Its chief executive Ben Rubin told the USA Today news site: "[We have] worked closely with the content owners and contacted users they alerted us about."
Meerkat's streams can only be watched live, while Periscope's remain online for playback for an additional 24 hours.
HBO and Showtime had attempted to restrict online piracy of the fight by obtaining a temporary restraining order, which forbade websites from publishing links to illegal free streams.
There had been speculation that the contest would beat the record 2.48 million pay-per-view purchases of 2007's Mayweather-Oscar De La Hoya bout.
Official figures for Floyd Mayweather Jr's defeat of Manny Pacquiao have yet to be published.
But the final tally may have been affected by glitches that made it impossible for some households to watch Saturday's earlier undercard fight, and led to a delay of the start of the main event.
"It was simply an unprecedented number of fans buying more amounts than we've ever seen in PPV history. So we had to slow down the telecast for orders to be processed," HBO told the New York Daily News.
The fight was screened by Sky Box Office for the cheaper price of £19.95 in the UK.
A spokeswoman for the broadcaster declined to comment.
However, the UK's Alliance for Intellectual Property urged new services to act responsibly.
"With the explosion in internet services comes great opportunity for consumers to access exciting content, whether sports, films, TV, music, games or books," the organisation's director general Eddy Leviten told the BBC.
"However, it is also vital that internet intermediaries act responsibly and ensure that creators and distributors are able to protect their creations and investments.
"Ultimately, this benefits everyone as great content continues to get made. Jobs and investment increases and choice is even greater for fans."