Canadian Michael Woods finished seventh in the stage and rose three spots to seventh in the overall standings.
"It's all small steps at this stage", Team Sky's Froome said about the six seconds he added to his advantage over Nibali, increasing it to 1 minute, 1 second.
Dutchman Wilco Kelderman (Team Sunweb), in fourth overall, Steven Kruijswijk (LottoNL-Jumbo) and Tejay van Garderen (BMC) are all strong time trialists and will be looking to gain seconds.
"It's still a good position to be in", said Froome, who is seeking his first Vuelta title.
"We chose to ride with Contador when he made a great attack, and I thought I had good legs and it all went off well", Lopez said.
"I take it one day at a time at the moment. There's just three days left and I hope we can get the job done".
GC contenders Vincenzo Nibali, who finished third on the stage, and Ilnur Zakarin both posted fine times, while Trek-Segafredo's Alberto Contador, 34, put in an outstanding performance for fifth place. But on a stage that began on the Circuito de Navarra and ended in Logroño, deep in La Rioja country, Froome showed he was still a ripe old vintage. Riders had to deal with many steep climbs and fast descents through narrow roads, including the ruthless final hill which brought them to a near halt as they tried to manage slopes with a gradient of up to 26 per cent. "I'm not taking anything for granted", he said. "I paced myself until today and I went all in".
Lopez, 23, claimed his first Grand Tour win on Wednesday last week when he won a similarly tough mountain stage finishing at the Calar Alto summit.
"I just have a huge, huge thank you for my teammates. It's fantastic. It's the best day of my cycling life".
The Vuelta ends Sunday in Madrid.