For the first time since its launch four months ago, the market share of Microsoft's search engine Bing slipped in September while that of its rival Google rose.
Bing's monthly market share in the US declined to 8.51 per cent in September from 9.64 per cent in August, according to web analytics firm StatCounter.
Similarly, the search engine's share globally decreased to 3.25 per cent last month from 3.58 per cent in August.
Microsoft launched Bing in May as part of its efforts to challenge the dominance of Internet major Google.
"Google was the beneficiary from the decline of its main rival, increasing (its US market share) by more than two percentage points to 80.08 per cent in September from 77.83 per cent the previous month," StatCounter said in a statement.
Microsoft has also joined hands with Yahoo! for a partnership mainly focusing on the Internet search market.
The statement said there was little consolation for Microsoft from the performance of its new partner, Yahoo! which also declined to 9.40 per cent from 10.50 per cent in August.
Globally too, Yahoo!'s market share dipped to 4.37 per cent in September from 4.84 per cent in previous month.
"The trend has been downwards for Bing since mid August. The wheels haven't fallen off but the underlying trend must be a little worrying for Microsoft," StatCounter's CEO Aodhan Cullen said.
Data is based on an analysis of 4.6 billion search engine referring clicks including 1.1 billion from the US.
A leading international web analytics firm StatCounter monitors more than 10 billion pageloads per month.
