Nairo Quintana was left frustrated as Chris Froome countered every attack he made on a gruelling stage 14 at the Vuelta a Espana.
The Movistar rider was desperate to increase his 54-second lead over Froome on the 196-kilometre route on Saturday, but was unable to shake his Team Sky rival.
Having negotiated the first three climbs together, Quintana opted to test the energy levels in Froome's legs on the Col d'Aubisque with a series of surges.
However, every time the Colombian opened up a gap the three-time Tour de France winner responded and was quickly back on his wheel.
A final attempt in sight of the summit finish also proved futile, leaving Quintana a little frustrated despite holding onto the leader's red jersey.
"We tried everything to drop Froome back, but in all of my final accelerations, he sooner or later bridged back to my back wheel," he told Movistar's official team website.
"It just wasn't possible this time.
"It was an intense day, a tough race where I think the team fared well. Even though I couldn't leave Froome behind, we're satisfied about the level of fitness we showed today.
"My calendar and Froome's has been pretty similar, in terms of wear and tear, this season, and also my legs feel tired at this point of the year... but I hope to keep it going into this final week, hopefully better than Chris, to conserve this leader's jersey."
Sunday sees the peloton face another summit finish up the daunting Formigal, and Quintana knows he will have to dig deep to stay in the lead.
He added: "Formigal will be surely a very, very intense day.
"We will have to wait until the break forms in the beginning - it's going to be a more explosive effort than today's - and then build our strategy for the finale, especially that last climb."