(Adds portfolio manager comment, updates prices to close)
* TSX ends down 101.13 points, or 0.71 percent, at 14,238.40
* Half of the TSX's 10 main groups fall
* Five declining stocks for every two gainers on index
By Alastair Sharp
TORONTO, Aug 13 (Reuters) - A slump in energy shares helped push Canada's main stock index to its third straight loss on Thursday as U.S. oil prices slid to fresh lows, though a Chinese central bank assurance on the yuan reduced some investor fears.
Energy stocks stumbled 3 percent as crude prices took another beating. U.S. crude prices were down 2.4 percent to $42.25 a barrel, while Brent crude lost 0.8 percent to $49.27.
In the group, Canadian Natural Resources declined 3.1 percent to C$30.96, while Suncor Energy Inc fell 1.7 percent to C$36.85.
"I don't believe oil can be at this level for a prolonged period of time," said Manash Goswami, a portfolio manager at First Asset Investment Management. "The big issue is that supply is still outstripping demand."
Crescent Point Energy shares ended off 1.6 percent at C$17.58, after the oil producer slashed its dividend, a move widely expected by investors who have recently punished the stock.
This week's devaluation of the Chinese currency pulled commodity prices down on concern China would not import as much.
On Thursday, China's central bank helped restore some calm to jittery global markets, saying there was no reason for the yuan to fall further given the country's strong economic fundamentals.
The Toronto Stock Exchange's S&P/TSX composite index finished off 101.13 points, or 0.71 percent, at 14,238.40. Five of the 10 main sectors fell, and there were more than five decliners for every two advancing stocks.
Retailer Canadian Tire Corp put more pressure on the market, tumbling 3.2 percent to C$126.31 after reporting lower-than-expected quarterly profit on slower sales growth.
"It's probably going to be challenging over the next few months. We're watching volatility very carefully," said Sid Mokhtari, market technician and director, institutional equity research, CIBC World Markets.
Financial stocks, which make up roughly a third of the index, weighed heavily, hurt in part by Canada's low interest-rate environment and by banks' ties to the battered oil and gas industry, Mokhtari said.
Toronto-Dominion Bank fell 1 percent to C$52.05. The overall financials group, which also includes life insurance companies, retreated 0.8 percent.
The materials sector, home to miners, gave up 2.4 percent, with gold miners leading the losses. Goldcorp Inc sank 4.5 percent to C$18.89.
Gold futures fell 0.8 percent to $1,114.40 an ounce, snapping five sessions of gains as the U.S. dollar firmed on U.S. economic data and easing concern over China's yuan.
$1=$1.31 Canadian Additional reporting by Solarina Ho; Editing by Peter Galloway and James Dalgleish