* Q1 EPS $1.79 vs est $1.81
* Q1 sales $2 billion
* Sees FY 2012 EPS $5.55-$5.75
* Shares fall 18 pct
May 17 (Reuters) - U.S. auto parts retail chain Advance Auto Parts Inc reported a quarterly profit that missed analysts' estimates, as h i gher supply chain costs hurt margins, sending its shares down 18 percent.
The company, which warned that sales trends in the second quarter remain challenging, said it expects annual comparable store sales to be in the low single digits for 2012. It also kept its full-year profit forecast of $5.55 to $5.75 per share.
Analysts on average were expecting earnings of $5.97 per share, according to Thomson Reuters I/B/E/S.
The company, which sells parts, accessories, batteries and maintenance items, also said it would repurchase $500 million of its stock. The new plan replaces the $300 million share buyback program authorized in August 2011.
Advance Auto Parts' first-quarter net income rose to $133.5 million, or $1.79 per share, from $109.6 million, or $1.35 per share, a year ago.
Sales increased 3.1 percent to $2 billion, helped by a 2.1 percent rise in comparable store sales.
Analysts were expecting earnings of $1.81 per share on sales of $2 billion.
Advance Auto Parts shares fell to a low of $67.22 in early morning trade on Thursday, making it the biggest percentage loser on the New York Stock Exchange.