ARAMON FORMIGAL, Spain — A surprise attack by Alberto Contador helped Nairo Quintana boost his lead over Chris Froome to more than three minutes after Sunday’s 15th stage of the Spanish Vuelta.

An audacious move by Contador’s Tinkoff team caught the peloton off guard with an attack at the start of the short 118.5-kilometer (74-mile) ride starting in Sabinanigo in the Pyrenees.

Quintana quickly joined Contador’s small breakaway that surprised Froome and isolated him from his Sky teammates, who were even further behind.

Quintana increased his 54-second advantage entering the day to 3 minutes, 37 seconds after leading the charge up the last of three ascents while Froome struggled to pursue.

Movistar’s Colombian climber crossed the finish line at the category-one Sallent de Gallego summit second three seconds behind stage winner Gianluca Brambilla of Italy, who took the win in 2 hours, 54 minutes, 30 seconds for his Etixx-Quick Step team.

“We were planning to make a move at the end of the stage, (but) Alberto is a great strategist. We joined forces and we pulled it off,” Quintana said. “It went better than I could have imagined.”

While Quintana rode strong throughout, Froome failed to close the gap without his teammates, who languished in the rear.

The three-time Tour de France winner finished the stage 18th — 2:37 after Quintana — and the damage could have been greater if not for the help of Astana leading the chase of the breakaway.

Contador said that he wanted to shake up the race after a disappointing stage on Saturday when he failed to keep up with Quintana and Froome in the French Pyrenees.

Taking advantage of the twisting, hilly terrain, the three-time Vuelta winner shattered the peloton with an attack only 13 other riders, including Quintana, could follow.

“After I crossed the line (yesterday) I could only think about today,” Contador said. “I looked at the route and I told myself that I had to try something.”

Movistar followed up with a second attack by Alejandro Valverde that eliminated all but one of Sky’s teammates, David Lopez, who soon spent his energy and faded.

Froome will still have the individual time trial, one of his strengths, on stage 19 to look toward.

Esteban Chaves remained in third place overall at 3:57 back, followed by Contador five seconds behind.

With the three-day mountain marathon over, Monday’s stage is a flat 156.4-kilometer (97.1-mile) from Alcaniz to Peniscola.

The 21-stage race ends in Madrid on Sept. 11.