* TSX ends up 0.18 percent at 11,888.08
* Potash Corp raised to "outperform"; shares up 5 pct
* All five big banks fall (Adds details)
TORONTO, Jan 5 (Reuters) - Toronto's main stock index ended at a 15-month high on Tuesday, led by a rally in shares of Potash Corp of Saskatchewan (POT.TO) after the big fertilizer company was upgraded to "outperform" [ID:nSGE6040FR] by Credit Suisse.
Potash Corp was the leading heavyweight advancer all through the session. It ended up 5.41 percent at C$123.00, which helped the TSX index reach its highest level since September 2008 and record its fourth straight higher close.
Prices for precious metals and crude oil were also higher, and while gold cut initial gains to turn lower, the overall tone to the index's energy and materials groups was solidly higher, and they rose 0.24 percent and 1.76 percent, respectively.
"There's follow-through buying from yesterday. The fact that the U.S. dollar is lower seems to help," said Elvis Picardo, analyst and strategist at Global Securities in Vancouver.
The Toronto Stock Exchange's S&P/TSX composite index .GSPTSE ended up 21.18 points, or 0.18 percent, at 11,888.08.
Financials were the loss leaders. Analysts cited profit-taking after the sector ran up sharply in December, while disappointing U.S. home sales data chipped away at sentiment about economic recovery.
Royal Bank of Canada (RY.TO) was the biggest drag on the index, falling 1.5 percent to C$55.75.
($1=$1.04 Canadian) (Reporting by Ka Yan Ng; editing by Peter Galloway)