* Expects Q4 revenue to fall 12-18 pct sequentially
* Q3 revenue up for the sixth straight quarter
* Shares fall 11 pct after-market (Adds CEO and analyst comments)
Oct 24 (Reuters) - Advanced Micro Devices Inc on Tuesday flagged competitive pressures with a forecast that pointed to the first revenue drop in seven quarters, sending the chipmaker's shares plunging 11 percent in after-hours trading.
The company, which has gained from a surge in demand for its chips from cryptocurrency miners, also sought to tamp down expectations of benefits from the boom.
"We're also predicting that there will be some leveling off of some of the cryptocurrency demand," said Chief Executive Lisa Su on a post-earnings call.
AMD's underwhelming forecast overshadowed a strong third-quarter performance, which was aided by a slew of launches this year such as the Epyc processors for servers and a new range of Ryzen desktop processors.
The company said it expects fourth-quarter revenue to fall about 12 percent to 18 percent from the third quarter. This implies a revenue of about $1.35 billion to $1.44 billion, according to Reuters calculation.
"AMD has headwinds with competition from Intel and Nvidia among other worries," Daniel Ives, chief strategy officer at GBH Insights said.
Bigger rival Intel Corp recently launched its new line of Coffee Lake processors, which analysts said could challenge AMD's Ryzen processors.
AMD's total revenue surged 25.7 percent to $1.64 billion in the third quarter, beating analysts' average estimate of $1.51 billion.
Sales in its graphics and computing business, which makes processors for servers and gaming consoles such as Microsoft Corp's Xbox and Sony Corp's PlayStation, surged 73.5 percent to $819 million.
"We anticipate seasonal demand to remain healthy as our customers enter the holiday sales cycle with Sony's PlayStation 4 Pro and Microsoft's Xbox One X," Lisa Su said on the call.
France-based company Atari said last month that its latest gaming console Ataribox would feature AMD's customised processor Radeon.
AMD reported a net income of $71 million, or 7 cents per share, in the quarter ended Sept. 30, compared with a loss of $406 million, or 50 cents per share, a year earlier.
Excluding items, the company earned 10 cents per share, topping analysts' estimate of 8 cents, according Thomson Reuters I/B/E/S.
AMD's shares have risen 25.7 percent this year, outperforming the S&P 500's nearly 15 percent increase but underperfoming the Philadelphia semiconductor index's 37 percent gain.
(Reporting by Laharee Chatterjee in Bengaluru; Editing by Shounak Dasgupta and Sriraj Kalluvila)