By Alasdair Fotheringham
POLSA, Italy (Reuters) - Italy's Vincenzo Nibali took a major step towards overall victory in the Giro d'Italia on Thursday after powering to his first stage win during this year's race in an individual uphill time trial.
Nibali more than doubled his overnight advantage over his closest overall pursuer, Australia Cadel Evans, from one minute 26 seconds to a more solid margin of four minutes and two seconds. Colombia's Rigoberto Uran remained third, four minutes 12 seconds back.
The last rider to start stage 18, the Astana rider surged home through to teeming rain on the 20.6 kilometer time trial from Mori to Polsa to beat Spaniard Samuel Sanchez by 58 seconds. Italy's Damiano Caruso was third, Uran finished sixth while Evans slumped to 25th, two minutes 36 seconds back.
"This is my first stage win here in 2013 and I and the team wanted to get this victory badly, I wanted to leave my mark on the stage wins as well as on the overall," said Nibali, who has finished second and third in previous Giros.
"But these are really important advantages, it means I can take things more easily. And so can my team. We can ride more calmly now."
The fastest at the mid-stage checkpoint by 32 seconds, Nibali's only blip was when he swerved late on one rain-sodden curve which appeared to slow him down.
"I felt good this morning even when I was doing a recon of the stage, so I thought I would be in good shape," he said.
"When the rain started, I had to be careful on the corners because I had high tire pressure, so I wouldn't slip."
Nibali admitted that he was surprised with the lead he had managed to open up over Evans.
"I was surprised that Evans wasn't in such good shape," the Italian said.
"I didn't know what his condition really was, he's been there or thereabouts throughout the stages but I thought he would do better today.
"He was my big reference point today, when I saw I was gaining time on him, I pushed even more."
The Giro now tackles two more stages in the Dolomites, although bad weather including subzero temperatures and freezing weather for Friday and Saturday could lead to some mountain passes being cancelled.
"There's a 70 percent chance that the course will be altered but we will reach a final decision tomorrow morning," the race's technical director Mauro Vegni told Italian television.
"Obviously with fewer climbs it would easier for me to control my rivals but either way I'm in good shape," Nibali said. "After today's stage, I feel a lot calmer."
The race finishes on May 26 in Brescia.
(Editing by Pritha Sarkar)