Bosses at The Guardian say first day sales of the new-look paper rose by 40 per cent - as a Midlands media expert predicted a fresh brutal battle for market share.
The new European-style Berliner - launched at a cost of £80 million a week ago today - is fighting it out on the news stands against compacts The Independent and The Times.
Carolyn McCall, chief executive of Guardian Newspapers, said: "Early reports suggest we have had a fantastic first day performance with a minimum 40 per cent increase in our headline sale.
" We invested a huge amount in encouraging readers to reappraise the paper. This has exceeded our highest expectations. We are delighted."
It would not reveal a day total sales figure or sales since the launch day, but editor of The Times, Robert Thomson, said he believed sales of the new-look paper were already dropping off after the first day flurry and he likened its look to an "instillation in the design museum".
He told The Birmingham Post: "There will no doubt be improvement as they (The Guardian) learn to cope with the new canvas, but the paper is yet to resolve the contradiction between aspiring to be an installation in the design museum and a success on the newsstand.
"At present, it has the feel of a product that was designed by designers for designers.
"An initial flurry is to be expected, given all the Guardian vouchers washing around in the market, but indications are that sales have already fallen sharply from the first day extravaganza."
Sales figures for August showed The Guardian prelaunch suffered a dramatic 6.26 per cent sales decline, to 341,698 copies.
In comparison the compact Times was up to 680,214 - a rise of 4.96 per cent.
Sue Heseltine, a senior journalism lecturer at the UCE in Birmingham, said she liked the look of the new Berliner and the fight was on in the new "qualities" market.
She said: "I think in the sort-term they may well see sales increase but the question is how does it fare in the long-term?
"There are pros and cons. "They can 'up' the story count per page in contrast to the compacts - for instance as I look here there are eight stories featured on the front.
"On the other hand they have the issue of the fold, and what is above and what is below on the news stands, which is difficult."
She predicted the compacts and the Berliner would thrash it out for a share of the same market and it was hard to predict a winner.
The Berliner format, favoured by many European newspapers including France's Le Monde, has been rolling off the Guardian's £50 million new presses for a week.
The relaunch also saw a complete redesign. The paper also became the first UK national to be printed exclusively in full colour.
The revamp took 18 months of planning and is reported to have cost a total of around £80 million.