The 2019 Tour de France winner began as one of the hot favourites for the pink jersey, but his form was uncertain as he continues to battle a long-term back injury, while he had not raced since finishing fourth in Tirreno-Adriatico in early March.

A late attack on the gravel roads of stage nine to the summit finish at Rocca di Cambio on Sunday gave Bernal a first career Grand Tour stage win and thrust him into pink, though things are far from decided with 11 stages to go and only 62 seconds separating the top 10.

"It's going to be a very intense second part of the Giro," Bernal said. "Up to now we have been fighting for seconds, but from here on the differences are going to be much bigger.

"We have to be very focused, the second part will be much harder.

"I don't know (about my form). I've not been able to do the training I wanted because of my back. It all depends on recovery."

Bernal has certainly looked in fine fettle, and was even competing for minor time bonuses in the second intermediate sprint on Monday - though Remco Evenepoel pipped him to second place to trim one second off his lead.

"When we started, we were aiming to lose as little time as possible," Bernal said. "If we lost up to a minute we would still be in a good position. So no, I wasn't expecting to be so active in the first week.

"The preparation has not been ideal, so to be fighting for stages and time bonuses, no, it was not in the plan. There has been emotion and adrenalin, and it has given us opportunities."

In their days as Team Ineos and Team Sky before that, the Grenadiers perfected the art of claiming the leaders' jersey in a Grand Tour by the first rest day and then effectively shutting down their rivals over the remaining days to claim victory.

But this Giro is still too close for defensive tactics to work as the bigger mountain tests loom - with Bernal adamant he needs a much bigger buffer heading into the closing time trial in Milan.

Saturday's stage 14 brings a climb of the mighty Zoncolan, while the biggest tests are reserved for next week's stage 20 to the Alpe Motta, which has two passes at more than 2,000 metres before the climb to the summit finish.

"I can't be attacking every day, but I need to get to Milan with something of a margin," Bernal said. "That's going to be the tactics. But we're in a great position, and can race calmly."

Bernal suggested he might need as much as a 90-second cushion over Evenepoel in a time trial, though the Belgian's form is even more uncertain than Bernal's - this is his first race since he fractured his pelvis in a dramatic crash off a bridge at Il Lombardia last August, and his first career Grand Tour.

Aleksandr Vlasov sits third, 22 seconds back, while others like Simon Yates remain in touch, with the Briton ninth, 56 seconds down.

"Any of the riders (are threats)," Bernal said. "I'm not ruling out Yates at all. In the last few years riders who have lost a lot of time have fought back. We have to watch a big group of rivals."

Yates himself said he was happy with how the first week of the race has gone, but the Team BikeExchange rider is less enthused about Wednesday's stage 11 to Montalcino, which includes 35km of the gravel roads familiar to fans of Strade Bianche.

"I would prefer not to have a stage like this in a Grand Tour," he said. "I believe there is a place for a one-day race like Strade Bianche, but not in a stage race - there is too much risk involved.

"Even guys who are technically good on gravel can have a puncture or crash that really affects the GC. For me, I'm not afraid of it, but I just hope to pass without incident."

Australian Associated Press