Zillow Group (NASDAQ:ZG) just released better-than-expected quarterly results, and the market is responding in kind.

After falling 3% in Tuesday's regular session, shares of the online real estate specialist popped more than 14% in after-hours trading when it told investors pro forma revenue rose 20% year over year to $171.3 million. Driving growth once again was a 29% pro forma increase in marketplace revenue to $145.5 million, including 37% growth in real estate revenue to $122.6 million, 44% growth from mortgages to $10.4 million, and a 21% decline in market-leader revenue to $12.5 million. Recall that Zillow previously announced that it's conducting a strategic review of market-leader business to determine whether to divest or integrate its software products, which were initially inherited as part of Zillow's acquisition of Trulia. Meanwhile, display revenue fell 15% to $25.8 million -- an equally unsurprising result given Zillow's decision to "underinvest" there in favor of growing its more promising agent advertising business.

In any case, Zillow's overall revenue exceeded the high end of its guidance range by $2.3 million and was well ahead of analysts' expectations for revenue of $168.8 million. That translated to an adjusted net loss of $0.01 per share, also significantly better than the $0.26-per-share net loss analysts were anticipating.

On integration progress
Zillow CEO Spencer Rascoff insisted last quarter that successfully integrating Trulia would be his company's "top strategic priority for 2015." As a result, I wondered in my earnings preview a few days ago how that integration is progressing.

According to Zillow, the short answer is "ahead of schedule." Rascoff elaborated:

We've been very focused operationally on the integration of Trulia, and made great progress on a number of fronts. As with most mergers of any scale, it has required a great deal of time, attention and energy. We're pleased to share today that we will have successfully combined all advertising products by the end of the third quarter, well ahead of the timetable we shared on our May 12th conference call. Most importantly, we believe the strategic rationale for the combination remains extremely strong, as we are already realizing benefits of our combined audience scale.

Zillow enjoyed 141 million average monthly unique visitors during the quarter to its four consumer-facing brands, including Zillow, Trulia, StreetEasy, and HotPads. And according to comScore, Zillow Group brands now represent a whopping 72% market share of all mobile exclusive visitors to the real estate category. In addition -- and keeping in mind Zillow purposefully let its direct MLS agreement with competitor-owned ListHub expire this past April -- Zillow Group has seen more than 300 MLSes sign agreements since January to send listings directly to Zillow and Trulia.

On the effectiveness of Zillow's marketing
Next, I wanted to hear more about the results of Zillow's previously unveiled plan to invest more than $100 million -- or roughly 15% of expected 2015 revenue -- in an enormous national advertising campaign designed to fuel growth and capitalize on the scale of its combined businesses. 

As it turns out, Zillow may not need to use all that cash to reach its goals. According to today's press release, adjusted EBITDA in the quarter nearly quadrupled year over year to $21 million, or 12% of total revenue and above its guidance for $17 million. Driving that outperformance, Zillow says, was a combination of "lower than expected advertising spend to achieve audience growth, integration related cost synergies, and better than expected revenue in the quarter." (Emphasis mine.)

On growth in (and loyalty of) agent advertisers
Next, I asked whether Zillow Group's base of agent advertisers was still growing not only in number, but also in loyalty.

Curiously, though, the answer to the former is "no" -- but with good reason. Zillow Group ended the second quarter with a total of 101,297 agent advertisers, down from 103,415 at the end of Q1. However, that sequential decline is largely the result of strategic decisions to end several of Trulia's short-term discounted products, as well as to change sales teams' incentives to focus on growing net revenue instead of the sheer number of advertisers. As a result, Zillow Group's average monthly revenue per advertiser rose almost 6% sequentially and 18% year over year to $375.

Perhaps more importantly, these agents are increasingly more loyal to Zillow as well. According to Rascoff during the subsequent conference call, the number of agents who spent more than $5,000 per month grew 48% year over year, while agents spending over $2,500 per month grew 44%, and the number spending more than $1,000 per month jumped 34% over the same year-ago period. What's more, the churn rate for these groups is very low, Rascoff says, "validating our strategy of focusing on high-performing agents."

On the scaling of rentals
I also wanted some fresh color on the progress of Zillow's burgeoning rentals segment, in which Rascoff expressed excitement given the scale provided by bringing Trulia into the fold. Remember, Zillow Group finished the integration of Zillow's and Trulia's rentals products last quarter and in June launched a new advertising solution aimed at multifamily partners called "Zillow Rent Connect: Boost." According to Rascoff, Boost has been "selling well," and Zillow Rentals' audience "remains massive, by far No. 1 in its category according to comScore despite competitors' ad spend."

Looking ahead
Finally, for the current quarter Zillow anticipates pro forma revenue in the range of $175 million to $177 million, and pro forma EBITDA $18 million to $19 million. Analysts, on average, were modeling a loss of $0.05 per share on slightly higher revenue of $180.9 million. 

For the full year 2015, however, Zillow reaffirmed its previous pro forma revenue guidance of $690 million and raised its pro forma EBITDA outlook to a range of $85 million to $90 million. Wall Street was anticipating full-year 2015 revenue of $666.5 million, and a net loss of $0.05 per share.

In the end, it's apparent that Zillow is inching toward sustained profitability, making better-than-expected progress in its integration of Trulia, and maintaining strong top-line growth from a number of sources with massive potential. In fact, I can't find anything not to like about this impressive performance, so I can't blame the market for so aggressively bidding up shares today.

Steve Symington has no position in any stocks mentioned. The Motley Fool recommends Zillow Group. The Motley Fool owns shares of Zillow Group. 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.