Shares in Trinity Mirror have jumped 15% after the UK newspaper firm said the demise of rival News of the World boosted declining sales.
Circulation of the Sunday Mirror jumped 55% in July after the hacking scandal saw NoW fold, separate data showed.
But the firm's sales and profits still continued their long-term decline in the first half of the year as a whole, the firm's interim results showed.
Profits before tax fell to £28.9m, with underlying profits down 17% to £41.9m.
Revenues dropped 2.9% to £371m in the 26 weeks to 3 July.
The firm has seen a steady decline in business since 2008.
But July trading suggests the NoW closure will provide a significant lift to group revenue.
"The benefits are evident in the improved group circulation revenues in July, which are up 2% year-on-year with our nationals up 4%, a significant improvement from the 5.4% decline in group circulation revenues in the first half," the company said.
Its Sunday national titles include the Mirror on Sunday, the Sunday Mail and the People, the last of which saw readership jump 46% in July compared with a year earlier.
But rival publications also did well, according to research firm ABC, with the Mail on Sunday up 15%, confirming it as NoW's successor as the most widely-read Sunday paper.
Shares in the Mail-owner Daily Mail and General Trust were more docile, rising just 4%.
The biggest winner was the Daily Star Sunday, with sales up 90%.
The newspaper is privately owned by publisher Richard Desmond, as is the Sunday Express, which saw sales rise 14%.
However, some NoW readers did not switch, with overall Sunday newspaper circulation down 7% from a month before. Moreover, NoW-owner News International intends to launch a new Sunday version of the Sun in the coming weeks.
Trinity Mirror's advertising revenues were down 4% for the six-month period, due in part to an 11% slump in July in the immediate wake of the News of the World closure.
However, the board said it anticipated that the improved trends in circulation figures seen in July would continue, although the company's overall performance for 2011 would still be in line with earlier expectations.
The firm may not itself be immune from the hacking scandal.
Three or four cases are due to be brought against the firm, according to lawyer Mark Lewis, who is representing a number of claimants, including the family of murdered schoolgirl Milly Dowler.
The firm said it was still too early to determine what impact there might be on its businesses from the public inquiry or an internal review of editorial controls.
"In addition the company has sought and received formal written confirmation from senior editorial executives... [that] they have not nor, to their knowledge, have any of their staff or anyone on their behalf, intercepted any telephone messages, made payments to serving police officers or accessed the police national computer."