• by Gavin O'Malley  @mp_gavin, May 15, 2013

Less than a year after putting Marissa Mayer at the helm of its shaky ship, Yahoo is sailing more smoothly than it has in years. 
 
According to fresh data, Yahoo.com replaced Facebook.com as the second-most-visited Web site in April. Month-over-month, Yahoo grew less than 1% to 164.4 million unique visitors, while Facebook’s monthly unique visitors dropped nearly half a percent to 164.1 million, according to Compete.

“It was a close race,” said Stephen DiMarco, CMO at Compete.

While Google (Mayers’ former employer) remained on top with 171.9 million unique visitors, the search giant also saw a decrease of a half a percent in April.

Along with traffic gains, Yahoo’s first-quarter earnings beat analysts’ expectations, while its stock price is up considerably since Mayer took over last summer.

By most measures, Mayer is still fighting an uphill battle, however. During the first quarter, Yahoo’s revenue was $1.14 billion -- down 7% year-over-year. Leave aside traffic acquisition costs, Yahoo said revenue was flat for the quarter at $1.07 billion.

Despite the loss in rank of its flagship site, Facebook should be soothed by the fact that Instragram.com -- which it bought last year for $1 billion -- broke the 25 million traffic mark for the first time April.

“This may only be a fraction of its mobile app use, but [it] shows Instagram’s momentum isn’t slowing down,” according to DiMarco.

As for what’s driving Instagram.com’s unique visitors, DiMarco suggested that the “nicer spring weather” is a factor. Indeed, Instagram’s desktop site grew 47% in March, followed by another 9% in April, according to Compete.

Also of note, 34% of Instagram.com’s incoming traffic came from Facebook, while 12% came from Twitter.

Another success story in April was LinkedIn.com, which drew a record high 35 million unique visitors during the month -- up 36% year-over-year.

CNN.com was the second-fastest-growing site with a 21% month-over-month jump – thanks to 28.6 million unique visitors -- while NBCNews.com may have grown less, although it had 34.5 million unique visitors.

The Huffington Post, meanwhile, had a small drop in traffic, but remained the most popular news source online in April.

Overall, Adobe was also the fastest mover in April, jumping eleven spots on Compete’s list of “Top 50 Sites.”

Adobe.com’s traffic increased 79% month-over-month, propelling the site from 27th on Compete’s list to 16th in April. Overall, Adobe attracted 65.5 million unique visitors during the month.

Compete says its findings are based on the Web activity of roughly 2 million U.S. consumers.