Bing's search share was up in June to 17.9 percent, while Yahoo dropped to 11.4 percent, according to comScore. The percentage Bing grew was exactly the amount of market share Yahoo lost.
This is another indicator the Yahoo-Microsoft search deal isn't meeting Yahoo CEO Marissa Mayer's expectations.
"One of the points of the alliance is that we collectively want to grow share rather than just trading share with each other," Mayer said earlier this year. "We need to see monetization working better because we know that it can and we've seen other competitors in the space illustrate how well it can work."
ComScore's monthly analysis showed Google holding steady market share from the previous month with 66.7 in June, but down slightly from June 2012's 66.8 percent.
Bing's share grew 0.5 percentage points from its 17.4 percent in May. In June 2012, 15.6 percent of searches were conducted on Bing.
Yahoo hit a new low as it lost 0.5 percentage points in June from 11.9 percent in May. Yahoo's market share is down overall from 13 percent in June 2012.
Both Ask and AOL had unchanged market share from May, with Ask at 2.7 percent and AOL at 1.3 percent. However, both are down from this time last year, where Ask had 3 percent of market share and AOL, 1.5 percent.
When it came to Google-powered organic searches in June, the search engine held steady from May with 68.6 percent of searches. Bing experienced a 0.1 percentage-point increase from May with 26.8 percent of searches.
Turning to "explicit core" searches, which exclude "contextually driven searches that do not reflect specific user intent to interact with the search results," comScore reported 19.2 billion explicit core searches in June, with Google ranking first at 12.8 billion. Bing came in second at 3.4 billion searches, followed by Yahoo at 2.2 billion. Ask saw 524 million and AOL, 253 million.