Nairo Quintana (Movistar) lit the fuse as the peloton hit the slopes of the brutally steep finishing climb on Stage 7 of La Vuelta, attacking several times and thinning down the front of the race to just a select few.
Primoz Roglic (Jumbo-Visma) and Lopez managed to claw the Colombian back, with a dogged Alejandro Valverde (Movistar) grinding away despite being distanced at times.
Eventually, Quintana realised that he wouldn't get a gap and set a good tempo for his team-mate to use his well-known explosive burst into the finish line to his advantage. Valverde duly delivered, moving himself up to third overall on a day that shook out the pretenders still high on the general classification and winnowed down the climbers at the top of the standings to a select few.
Lopez sits on top after attacking a strong team time trial and his performance attacking away from the peloton on Stage 5, but will be feeling the pressure from behind as Roglic (six seconds), Valverde (16 seconds) and Quintana (27 seconds) all lie well within striking distance.
"I can’t say that this climb suited me well as it was a steep and explosive powerful climb," said Lopez. "However, I gave my best today and I think I can be happy with my performance.
"Finally, we remained four in the lead, everyone tried to do something, but it was impossible to gain terrain on these steep slopes. I expected that Alejandro Valverde would be a big favourite today as this climb suited him perfectly.
"Anyway, once again I am in the red jersey and I am happy with it. We did a good stage and it is nice to come back into the lead. On Sunday we will have another very hard day and, I think, the climb in Andorra will suit me much better. So sure, with the whole team we will keep on fighting in this Vuelta day by day."
Stage winner Valverde was emotional after his stage victory, showing the import of the result in the context of his storied career.
"I'm so, so happy," said Valverde. "This season has already been good to me, always up there within the best, but taking a stage like this one in La Vuelta, with such a strong competition - it really makes me happy.
"I want to thank all of my team-mates for the huge gamble they made on us for the win, and Nairo in particular, because he rode brilliantly over the last climb. He tried to distance Roglic and López with his attacks, but seeing they were able to match him, he set a steady pace so I could go for the victory later on."
"I was confident, I knew I was doing well, and the worst result I could have got was fourth," Valverde joked. "I just tried to keep the moves under control, and I knew I was the fastest of the three, so I remained calm until the end. It's still a long way to go in this Vuelta, but for the time being, it seems like we two, Nairo and myself, are within the top four contenders for the GC win at this specific point.
Valverde won the Vuelta back in 2009, while his team-mate Quintana took out the 2016 edition. The pair will be looking for better cooperation than the Movistar top guns have managed in the past, with general classification contenders appearing to ride their own race at times at odds with the tactics of others in the same team.
"Aiming to win this? Of course, it would be incredible to take the victory, 10 years after my first one, but I must remain realistic," said Valverde. "What there isn't is a single problem between us. Nairo said he wants me to be the team leader, but I think he must not rule himself out of contention at all.
"He's doing really well, and he's talented enough to aim for this victory. At Javalambre on Wednesday, there was some controversy from Colombia about me pulling Roglic, but the thing is, if I didn't have López riding away from us, I wouldn't have ridden that way. I couldn't lose time against him, since he's so dangerous. Roglic has proven to be really strong, too, and he should be the best of us four at the time-trial, but anything can happen."
The next big challenge for the GC hopefuls is the climbing-filled Andorran Stage 9 which will be immediately followed by the rest day, incentivising attacking riding on the tough parcours.