What: Shares of Zillow Group, Inc. (NASDAQ:Z)(NASDAQ:ZG) rose 13.2% in the month of September, according to S&P Capital IQ data, after it completed its integration of Trulia and sold its Market Leader business. Zillow Group stock has continued to rally so far in October, as well, leaving it up nearly 37% since the beginning of last month, and helping investors absolutely crush the S&P 500's respectable 5.5% return:

Z Chart

Z data by YCharts.

So what: Zillow started the month strong by announcing the sale of its Market Leader CRM software business to Constellation Software for $23 milllion. But this wasn't entirely shocking; Zillow inherited Market Leader as part of its acquisition of Trulia earlier this year, and struggled to find ways to help it mesh with the combined companies' strategic vision since then. In April, Zillow told investors that, while it was no longer actively selling Market Leader Products, it would continue to support existing customers as it considered whether to integrate or divest the company.

While some investors may have been concerned about the small sale price -- Trulia itself acquired Market Leader in 2013 for $355 million -- I explained shortly after the release that Market Leader is considerably smaller today due to prior layoffs during the integration, as well as Zillow's sale of Market Leader subsidiary ActiveRain to the Ben Kinney family of companies earlier this year.

But more significant to Zillow's long-term success is its now-completed integration of Trulia, which was capped by the formal combination of Zillow's and Trulia's agent advertising platforms. Shortly after that happened, Zillow Group also launched its new "Premier Agent" advertising platform, which enables agents to seamlessly buy and manage ads across all four of Zillow Group's brands including Zillow, Trulia, Hotpads, and StreetEasy. In doing so, Zillow has drastically increased both the ease of use and value proposition of its real estate advertising solutions, which already comprised 77% of total sales (excluding Market Leader) after increasing 37% year over year last quarter.

Now what: Zillow Group isn't set to announce third-quarter 2015 results until early next month. But if the recent rise and last quarter's impressive report are any indication, it seems safe to say the market has high hopes for Zillow as it works to increase its slice of the $13 billion that real estate agents spend annually advertising their listings. With its combined ad platform in place, and with Market Leader finally in new hands, I think Zillow Group is better poised than ever to capitalize on that opportunity.

Steve Symington has no position in any stocks mentioned. The Motley Fool owns shares of and recommends Zillow Group (A shares) and Zillow Group (C shares). Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.