Nairo Quintana stamped his authority on the Giro d'Italia when he claimed the overall lead by winning the first big mountain stage that was marred by a controversial motorbike incident on Sunday.

Defending champion Vincenzo Nibali was also dealt a big knock when he cracked on the final climb, a punishing 13.6-km ascent up the Blockhaus.

Team Sky's Geraint Thomas and Mikel Landa and Orica-Scott's Adam Yates were both brought down in a crash at the foot of the climb when a stationary police motorbike at the side of the road caused a big pile-up.

Thomas, who appeared to be suffering from a right shoulder injury, needed a couple of minutes to get back on his bike.

Ireland's Philip Deignan played a key part as Thomas attempted to limit his losses, helping his team-mate recover up the mountain.

Yates finished four minutes 38 seconds behind and Thomas's ordeal ended 5:07 after Quintana had crossed the line.

Thomas said: "It's ridiculous. That shouldn't happen. We were all racing for the bottom of the climb.

"Next thing I know someone in front of me hits the motorbike, we go down. My shoulder popped out (of its socket) as well.

"I felt good, then I crashed. That was it. Race over. It's really disappointing. I'm a bit angry at the minute."

"These things happen in sport," said Team Sky principal Dave Brailsford. "You've just got to stay calm and not over-react. Obviously theres emotion but my role here is to keep the guys calm, assess the situation and look at how we go on from here.

 "A motorbike shouldn't have been there. I'm sure the guy who was riding the motorbike realises that too. We fight on. That's it."

Colombian Quintana (Movistar), looking to win his second Giro title, made the decisive move 4.7 km from the finish line of the 149-km ninth stage from Montenero de Bisaccia, dropping Frenchman Thibaut Pinot (FDJ) and Nibali (Bahrain-Merida).

Pinot limited the damage to take second place, finishing just ahead of Dutchman Tom Dumoulin (Team Sunweb), 24 seconds off the pace.

Nibali was fifth, a minute behind Quintana.

Overall, Quintana leads second-placed Pinot by 28 seconds and third-placed Dumoulin by 30 seconds, but the Dutchman a blow when key lieutenant Wilco Kelderman, the man who initially ran into the moto, was forced to retire after suffering a broken finger.

Another Dutchman, Bauke Mollema (Trek-Segafredo), who was fourth on the day, is fourth overall 51 seconds off the pace and fifth-placed Nibali is 1:10 behind Quintana.

Monday is a rest day and Tuesday's 10th stage is a 39.8-km individual time trial that should see Dumoulin, originally a time-trial specialist, gain time on his rivals.