The commercial broadcaster revealed a slight 3% increase in revenues to £1.03bn in its interim results for the period ended 30 June.
ITV said net advertising revenues slipped an estimated 1% in the first eight months but would likely drop 20% percent in September.
The overall market is set to drop 17% in September because of falling adspend and tough comparisons with last September, which was buoyed by the broadcaster's coverage of the Rugby World Cup.
ITV said: "On current estimates, the television advertising market has weakened in September, where tough year-on-year comparisons apply, given the Rugby World Cup in 2007.
"Whilst ITV has limited visibility on advertising revenues beyond September, ITV expects to outperform the total market over the full year."
ITV is forecasting the total advertising market in the third quarter to fall by around 9%.
The ITV board said it has reassessed its turnaround strategy, which executive chairman Michael Grade is spearheading, in the light of the weaker advertising and economic outlook.
Part of that strategy has seen ITV invest in more high-quality programming and it has had some successes with the latest installments of 'Agatha Christie's Marple', starring Geraldine McEwan, and new medical drama 'Harley Street', starring Paul Nicholls.
Looking ahead ITV has 'Marco Pierre White's Great British Feast', 'Griff Rhys Jones' Great Cities of the World', more 'Britain's Got Talent' and 'Undress the Nation'.
"The board remains confident that the turnaround strategy will deliver sustainable, long-term growth and is therefore maintaining its investment in programming," the board said. "However, given the market uncertainty, ITV is revising its global content and online targets."
Globally ITV is seeking to increase its annual revenues through organic growth and acquisition, to a run-rate of £1bn by the end of 2012. The previous target was to double revenues to £1.2bn by 2012.
It has also extended the time frame for its online revenue target of £150m by 2010 to 2012. ITV said the change to the previous target of £150m online revenues by 2010 also reflects regulatory delay to the planned Kangaroo service.
Additionally, ITV said the group is targeting an extra £35m of cost savings by the end of 2010.
It said it was already on track to deliver £41m in savings by the end of 2008 and £40m of additional regional savings from the end of 2009.
Grade said: "We cannot control the economic environment in which we operate. As a result of the recent slowdown in the television advertising market, the board has taken some tough decisions which are reported here today.
"We are committed to maintaining investment, notwithstanding the cyclical downturn. By holding our focus on delivering the Turnaround Strategy, we are confident ITV will be strongly positioned to grow as the economy recovers."
Earlier this week, it was reported that ITV's 6000-strong headcount could be reduced by as much as 10% as part of a cost-cutting measure.
The job cuts are expected to hit the production and advertising sales areas of the company, after ITV drafted in Boston Consulting Group to assess efficiency.