DETROIT (AFP)--Microsoft Corp. (MSFT) chief Steve Ballmer on Wednesday downplayed expectations for the success of the newly launched Bing search engine, but said the company was committed to challenge Google Inc. (GOOG)over the long-term.

"When you're sitting there as we are in the search base, you've got 8% market share and there's a kind of a big dog competitor out there in the market place, you can do very big things," Ballmer said.

The initial response to Bing has been "very good" Ballmer said, but it won't displace Google anytime soon.

"I don't want to overset expectations. We're going to have to be tenacious and keep up the pace of innovation over a long period of time," Ballmer told an economic summit in Detroit, Michigan.

"We may be successful, we may not, but we can't be successful without being committed to changing things, changing the approach, changing the business model and you can't give up in six months, or a year or two years."

Microsoft said Bing, unveiled at the end of May, is designed to intuitively understand what people are seeking on the Internet and challenge online king Google.

The U.S. software colossus described Bing as a "Decision Engine" aimed at helping people make buying decisions, plan trips, research health matters or find local businesses.

Bing's launch came in the wake of Google and Yahoo! Inc. (YHOO)announcing refinements to their search services and the launch of a Wolfram Alpha query engine that delivers answers instead of lists of Web sites.

Bing replaces MSN Live Search, which has languished in a distant third place behind market-leading Google and second-place Yahoo.

Bing relies predominately on algorithms and key words to provide results for online searches but has infused some semantic technology that deduces intended meanings of phrases, according to Microsoft.

Ballmer declined to comment on what Bing's launch meant for Microsoft's attempt to acquire Yahoo.

Online tracking firm comScore Inc. (SCOR) said Wednesday that Microsoft saw its share of search result pages in the U.S. continue to climb during the second week of Bing's introduction.

Microsoft Sites' share of search result pages in the U.S. increased to 12.1% June 8 to 12, up three percentage points from the May 25 to 29 period prior to Bing's introduction, comScore said.

Microsoft's average daily penetration among U.S. searchers also increased by three percentage points to 16.7% during the work week of June 8 to 12, comScore found.

ComScore on Wednesday also released U.S. search engine rankings for May, before Bing's introduction.

Google grabbed 65% of the U.S. search market for the month followed by Yahoo with 20.1% and Microsoft with 8%.