Google Maps slipped last year, giving Facebook enough room to become the most popular mobile app in the U.S., according to ComScore.
Facebook's mobile app had nearly 85.5 million unique visitors in December, while the Google Maps app had 74.6 million users, according to ComScore. Facebook first began to surpass Google Maps in September.
The research firm placed part of the blame for Google Maps' slip as the No. 1 app at Apple's feet.
"Apple's decision to replace Google Maps with Apple Maps on iOS 6 also caused a decline in Google Maps usage in October, which is largely responsible for the position swap," wrote Andrew Lipsman, a ComScore analyst. "Meanwhile, Google Maps has been clawing its way back the past few months after getting reinstated on iOS 6, so look for the competition for the No. 1 spot to heat up as we head into 2013."
However, while Google might have slipped out of the top spot, other Google apps swept the remaining spots in the top five.
Google Play, with more than 61 million unique users in December, came in third place. The Google Search app, with more than 60 million users, was in fourth place, and Gmail, with nearly 54 million users, was No. 5.
However, despite the number of Google apps in the rankings, Facebook is dominant in how much time users spend on the app.
"ComScore's numbers show that Facebook's mobile app accounts for 23% of time spent on apps," wrote Lipsman. "All of Google's apps combined account for 10% of time spent. This means more than one out of every three minutes spent on mobile apps is spent on Facebook or on a Google app."
Sharon Gaudin covers the Internet and Web 2.0, emerging technologies, and desktop and laptop chips for Computerworld. Follow Sharon on Twitter at @sgaudin and on Google+, or subscribe to Sharon's RSS feed . Her email address is firstname.lastname@example.org.