TORONTO (Reuters) - Toronto's resource-heavy main stock index tumbled yesterday for a third straight session, dragged lower by a slide in oil, as fears intensified that Greece's debt crisis could spread to other euro zone countries and derail economic recovery.

The drop was led by the heavyweight energy sector, down 3.05 percent, as the unfolding Greek crisis pushed the price of oil below $80 a barrel for the first time since late March.

In the oil patch, Suncor Energy dropped 5.44 percent to C$32.51, while Canadian Natural Resources sank 4.05 percent to C$73.83.

The Toronto Stock Exchange's S&P/TSX composite index closed down 155.73 points, or 1.29 percent, at 11,875.13. Earlier, it touched a low of 11,754.28, its weakest level in nine weeks. Eight of its 10 sectors were down.

Protesters in Athens clashed with police over austerity measures, while policy makers warned of the dangers of contagion in other high-debt euro zone nations, sending global stocks and commodity markets lower.

"The market's concern is: are these sovereign debt concerns going to slow down or derail the economic recovery, initially in Europe, but overall, globally, and as a result commodities are pulling back," said Anil Tahiliani, head of research at McLean & Partners Wealth Management in Calgary.

The price of gold rebounded from one-week lows on a return to safe-haven buying, helping to reduce the losses in the TSX materials group, which finished down 0.27 percent.

Barrick Gold rose 0.52 percent to C$44.13, while base metals producer Teck Resources gained 0.51 percent to C$37.44. But fertilizer producer Potash Corp fell 1.7 percent to C$105.01.

HudBay Minerals dropped 4.82 percent to C$11.45 after it reported a weaker than expected first-quarter profit late on Tuesday.

Agrium shares cut losses to finish 0.71 percent lower at C$61.36 after the fertilizer maker reported a quarterly loss.

Another weak spot was the hefty financials group, which shed 1.26 percent.