Thomas loses lead in France
Carlos Betancur seized the overall lead of Paris-Nice from Geraint Thomas by climbing to a second successive victory of the race on stage six.
The Colombian reached the top of the short and steep ascent to the finish in Fayence just behind Rui Costa and then rounded the world champion at the death.
Zdenek Stybar, Thomas and Arthur Vichot followed three seconds later to take third, fourth and fifth respectively following a keenly fought finale between the leading contenders for overall victory.
Betancur (Ag2r-La Mondiale) collected ten bonus seconds for his win, meaning he overturns his five-second overnight deficit to Thomas and now leads the Team Sky rider by eight seconds in the general classification. Costa (Lampre-Merida) climbs to third overall, a further ten seconds back.
Betancur said afterwards: "I knew it was going to be long day, with a lot of kilometres, but that the finale suited me. My Ag2r team were very cohesive and this is the result of their great work. It would have been difficult to do better than we did today.
"I think Geraint Thomas remains one of my most dangerous rivals, as well as [Vincenzo] Nibali but Ag2r are among the best teams to help me in the mountains and to defend the yellow jersey."
Stage six was the longest of the race, at 221.5km, but was decided on the testing category-two climb to the finish line in Fayence, just west of Nice, which included ramps of over 20 per cent in gradient.
The peloton had already been whittled down to an elite group of around 40 riders by the time they hit the foot of the ascent, and David Vuillermoz (Ag2r-La Mondiale) mounted the first attack about 1.2km out as he looked to lure team-mate Betancur's rivals into action early.
Final climb decisive
The move put Thomas under pressure to chase and when he began to tire about 500m out, Tom-Jelte Slagter (Garmin-Sharp), who was third overall, looked to capitalise by launching his own bid for the line.
The Dutchman suffered the most untimely of mechanical problems, though, about 150m out, which opened the door for Costa to surge forward, this time decisively.
Betancur was the only man who could follow and the Colombian still had enough energy to steal victory on the line.
Thomas, meanwhile, staged a fine recovery by driving back through the pack when the incline relented and only narrowly missed out on pipping Stybar (Omega Pharma - Quick-Step) to third.