Betancur at the double in Paris-Nice
Colombia's Carlos Betancur Gomez celebrates on the podium at the end of the sixth stage of the Paris-Nice cycling race, on March 14, 2014, between Saint-Saturnin-les-Avignon and Fayence - by Eric Feferberg
It was the second straight stage win for Betancur who overtook Portuguese world champion Rui Costa in the last 100 metres on a steep summit finish.
Czech rider Zdenek Stybar crossed in third three seconds behind the leader and ahead of Britain's Geraint Thomas, who had been wearing the leader's yellow jersey.
With a 10sec time bonus for winning the stage, Betancur wiped out the 5sec deficit to Thomas that he began the day with and turned it into an 8sec lead.
But Betancur did not sound confident he would be able to hold on until the Promenade des Anglais in Nice.
"That was a long stage, there were a lot of kilometres and I had to wait until the end," he said.
"In the overall standings there are a lot of riders close to me, and I'm starting to feel the fatigue."
Costa was delighted to have finally been able to show his hand and demonstrate his victory potential.
"Congratulations to Betancur. I saw the finish nearing and I knew I'd gained a good advantage but Carlos pulled off a very tough comeback.
"It was only with great legs that he managed to beat me."
The final climb was a gruelling 1,200 metres with a 10 percent gradient after the 221.5km stage.
French rider Alexis Vuillermoz attacked on the final ramp with Dutchman Tom-Jelte Slagter and Costa setting off in hot pursuit, while Betancur slipped in behind the world champion.
Vuillermoz, Betancur's AG2R teammate, saw his victory hopes dashed as he fell on the final bend while Slagter suffered a mechanical problem as he tried to avoid the fallen Frenchman, ruining his chances both of the stage win and an overall success.
Slagter had begun the day in third overall at just 4sec but his bad luck cost him 1min 34sec and all chance of victory in Nice as he trailed in 39th on the stage.
Costa seemed set to benefit as he showed his hand for the first time in this race, only for Betancur to pass him in the finale.
Betancur had said following his victory on the fifth stage on Thursday that he felt this one would be the decisive stage and so it proved for many riders.
One such was Giro d'Italia champion Vincenzo Nibali who had attacked on the descent of the Col de Bourigaille in the final 20km but then lacked the legs on the final climb and lost 41sec as he came in 35th.
One surprise was that of Spaniard Jose Joaquin Rojas who kept in touch with the leaders and finished the stage in 14th, just 11sec back, to maintain fifth place overall.
Costa moved up to third at 18sec with Stybar fourth at 22sec.
Saturday's seventh stage covers 195.5km between Mougins and Biot Sophia Antipolis, and includes five climbs.