* PC sales down 1.1 percent in Jan-March
* HP, Acer, Dell see dips
* Post-holiday decline, tablets, Japan blamed
* Gartner still sees annual growth
SEATTLE, April 13 (Reuters) - Computer sales slid lower in the first three months of this year for the first time since 2009 as shoppers suffered post-holiday shopping fatigue, Apple Inc's (AAPL.O) iPad continued to attract buyers and Japan focused on recovering from the earthquake and tsunami.
The world's biggest personal computer (PC) makers, Hewlett-Packard Co (HPQ.N), Acer Inc (2353.TW) and Dell Inc DELL.O all saw year-on-year declines.
The dip is a warning sign for chipmaker Intel Corp (INTC.O) and software giant Microsoft Corp (MSFT.O), whose fortunes are closely tied to growth in the PC market.
PC sales fell 1.1 percent in the first quarter to 84.3 million worldwide, according to tech research firm Gartner, well short of its forecast for 3 percent growth.
The dip was the first since the second quarter of 2009, when most of the world was still in the grip of economic turmoil.
"Although the first quarter is traditionally a slow one for PC sales, these shipment results indicate potential sluggishness, not just a normal seasonal slowdown," said Gartner, in a statement.
The research firm said sales were dragged down by a weak consumer segment, as shoppers resisted low prices on PCs or switched to buying tablet devices such as Apple's iPad instead.
Business demand for computers was much stronger, said Gartner, and likely to last another year as companies replace old machines.
Japan was a particularly weak spot, with PC sales falling 13 percent in the quarter, as people focused on getting back to normal after the March 11 earthquake and tsunami rather than spending money on new technology.
Gartner still expects worldwide PC sales to grow 10.5 percent to 388 million units this year, although that is well below its forecast of 15.9 percent growth, made in November.