Alphabet Inc. (GOOGL - Get Report) shares are set for their biggest single-day decline in nearly seven years Tuesday after the online advertizing giant posted softer-than-expected first quarter sales growth and failed to convince investors on a conference call that the slowdown will abate over the coming months.

Google said revenues for the three months ending in March was pegged at $36.3 billion, a 17% advance from last year but the slowest rate of growth in three years and a figure that missed analysts' forecasts of a $37.322 billion. Stripping away payments to distribution partners, Google said, revenues rose to $29.5 billion, just shy of the $30 billion forecast.

The group's adjusted bottom line remained solid, rising 23% from last year to $11.90 per share and easily topping Street forecasts, but a $1.7 billion EU fine linked to anti-competitive ad practices, as well as a surging expenses growth rate of 16.5%, highlight risks in the group's global business model.

"In terms of our key revenue drivers, with respect to Sites revenues, as we indicated last quarter, the timing of product changes in ads at times can have an impact on year-on-year growth rates,£ CFO Ruth Porat told investors on a conference call late Monday. "We will continue to make changes with a focus on the long-term best interest of users and advertisers."

"We remain confident about the sizable opportunity ahead to improve the advertiser and user experience through our ongoing commitment to product innovation, in particular by leveraging machine learning across our ads products and properties," she added.

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Google shares were marked 8.26% lower at the start of trading Tuesday to change hands at $1,189.51 each, the lowest since April 1 and a move that would trim the stock's year-to-date gain to around 14.8%.

The sharp share price decline was partly influenced by management's reluctance to peg the revenue growth slowdown to anything more specific than currency fluctuations and increasing competition.

I think if I could just maybe expand on the investing phase, as we are looking at the phase of investing and supporting growth around the globe, what we are really looking at is what's needed to support long-term revenue and earnings growth," Porat said. "The operating margin did benefit, and as I noted in my opening comments that, from the fact that Q1 marketing expense, growth moderated, but that was the timing issue."

"We do expect to pick up in marketing expense in the second quarter and other than that really nothing to comment on," she added.

"As the benefits from the investments Google continues to incur toward generating new streams of revenue are nontransparent, we suspect that from a tactical perspective the bear argument that it needs to spend to maintain growth in its current businesses will get louder," said Credit Suisse analyst Stephen Ju, who has an 'outperform' rating with a $1,296.00 price target on the stock.
 
"With that in mind, we note that while the Street has implicitly modeled the costs around the company's various longer duration products, revenue is yet to come - we hence remain buyers of GOOGL shares on that optionality." he noted.