Silicon Valley, the world is your playground -- enjoy it while it lasts. Google and Facebook still dominate the global digital advertising market, but they’re seeing increased competition from four major Chinese tech companies, according to researcher eMarketer, which included market-share estimates from those companies for the first time in a report released on Tuesday.  

The four companies -- Baidu Inc., Alibaba Group, Tencent Holdings Ltd. and Sina Corp. -- are expected to take 10.55 percent of the worldwide digital ad spend in 2014. The lion’s share of that will go to Baidu and Alibaba, which are expected to take 4.68 percent and 4.66 percent of the market, respectively. That’s nearly double the share earned by Microsoft Inc. and Yahoo Inc. and light years ahead of Inc., AOL Inc., LinkedIn Inc. and Yelp Inc.

Bryan Wiener, chairman of the ad agency 360i in New York, said the report drills home the importance of China as an emerging market for digital ads. Advertisers looking to reach consumers there will have no choice but to pay attention, he said.  

“If you have a Chinese strategy, you’re going to be spending an increasing amount of money with Alibaba and Baidu,” Wiener said.  

He said the explosion of e-commerce and the smartphone market are amplified in China, a country of 1.3 billion people where strict policies on Internet censorship give advertisers little choice but to buy home-grown companies like Baidu and Alibaba.

“Facebook, Twitter, YouTube -- these things are blocked in China,” Wiener said. “So the bigger China becomes as a market for advertising, not only are [Alibaba and Baidu] going to become bigger players, but for the traditional players, it’s going to shrink their share.”

Fortunately for everyone involved, it’s a growing pie. Global digital advertising is expected to grow 21 percent this year to $146.4 billion. Emerging Chinese giants notwithstanding, Google still dominates with 31.1 percent of the total market, down slightly from 31.55 percent last year.

On mobile, Facebook gained the most ground, going from 16.6 percent in 2013 to 18.4 percent this year, while Google’s mobile market share slipped from 46.6 percent to 40.5 percent.  

Alibaba, which is coming off its record-breaking $25 billion initial public offering in September, is now the fourth-largest digital ad seller in the world. But Rob Norman, chief digital officer of GroupM, the media-buying division of WPP, said Alibaba could face challenges with the growing penetration of smartphones, whose smaller screens are notoriously more difficult to monetize.

“Like Google, a rapid transition to mobile and the limitations that places on available advertising inventory may act as a brake on Alibaba’s growth,” Norman said.

Read the full eMarketer report here.

Christopher Zara is a senior writer who covers media and culture. Got a news tip? Email me here. Follow me on Twitter @christopherzara.