The speed with which Comcast's Brian Roberts returned with a higher offer was designed to show how determined he is to buy the group which is present in 23 million homes across Europe.
A person familiar with the situation said Comcast believed the deal would still be accretive to its cash flow in the first year of completion at the new price it had offered.
Sky's shares were up 3 percent at 15.38 pounds on Thursday, valuing it at 26.6 billion pounds, or $35 billion, as investors bet the battle has further to run for a group which owns a slate of top sport and original drama content.
"Investors are now close to doubling their money as a result of the bidding war for Sky, and there may yet be another twist in this tale which will swell their coffers even more," Laith Khalaf, a senior analyst at Hargreaves Lansdown said.
Sky's shares have risen 95 percent since Fox made its first bid in 2016, and have risen 55 percent in the last year.
The fight for Britain's leading pay-TV group is part of a bigger battle being waged in the entertainment industry as the world's media giants spend tens of billions of dollars to take on the rapid growth of Netflix <NFLX.O> and Amazon.com <AMZN.O>.
Comcast and Walt Disney <DIS.N> are locked in a separate $70 billion-plus battle to buy most of Fox's assets, which would include Sky, and Disney is backing Murdoch in his pursuit of the British company.
The stand off pits the industry's biggest names against each other, with Roberts, the Murdoch family and Disney's Bob Iger engaged in a multi-billion dollar game of chess to reshape the global entertainment business.
The three are at a tech conference in Sun Valley, Idaho.
Analysts are divided as to who will emerge triumphant.
Jeff Wlodarczak at Pivotal Research Group said Comcast may succeed in winning Sky but lose out on Fox to Disney.
Richard Greenfield at BTIG said however he thought Disney needed to buy Sky to secure a direct relationship with customers in Europe so it could sell them its vast range of programming.
Murdoch helped to launch Sky in 1989 in Britain, building it up to be Britain's dominant pay-TV provider through its ownership of Premier League soccer, U.S. drama and films. It now offers satellite TV in Ireland, Austria, Italy and Germany, and streaming services in Spain.