Riche Porte (Team Sky) lost a further 12 seconds to Michal Kwiatkowski (Omega Pharma-QuickStep) on the climb to the centre of Arezzo but warned that Saturday's long mountain finish could see far bigger gaps open up and so produce a shake-up on the overall standings at Tirreno-Adriatico.
Porte slipped to 16th overall, 39 seconds down on Kwiatkowski. Alberto Contador (Tinkoff-Saxo) is only three seconds closer to the young Polish rider and is widely expected to attack to try and win the stage and try to grab the overall lead.
Porte is convinced Saturday's 240km and the 14km to the finish will be more important than Sunday's short but 22 per cent climb to Guardiagrele.
"I've seen the video of tomorrow's stage (Saturday) and it's going to pretty decisive, even more so than Sunday," Porte predicted.
"Sunday's finish is steep but the time you can loose on a short climb like that is not usually the same as the long climb up to the finish at Selvarotonda.
The flip side is that you can gain more time on climbs like that. I'm confident. It'd be nice to claw back some time. 27 seconds in the team time trial is a fair bit to loose. But there's not much we can do about that. We can only take it as it comes."
Porte was expected to lead Team Sky at Paris-Nice and try to defend his 2013 victory but made a late switch to Tirreno-Adriatico after Chris Froome pulled out due to a back problem. Tirreno-Adriatico has a far harder parcour than its French rival but Porte is quietly confident about his climbing form.
"My training has been going really well recently. I've been based in Monaco, doing some longer climbs, so I'm quite happy with where I am at for this year," he said.
Tirreno-Adriatico is an important test for Porte and Team Sky before this year's Giro d'Italia. Porte will lead the British squad in Italy this year, hoping to follow on from Rigoberto Uran’s solid second place overall and avoid the problems that afflicted Bradley Wiggins' failed assault for the maglia rosa.
Porte knows Italy well after racing successfully here as an amateur. He finished seventh in the 2010 Giro d'Italia, his Grand Tour debut.
Success at Tirreno-Adriatico would make him an automatic favourite for the Giro d'Italia but he explained that any stage race victory would boost his morale for May.
"I don’t think you need to win Tirreno-Adriatico to prove myself but it would be great for morale," he said.
"I don’t think you can be too picky between races like Tirreno or the Volta a Catalunya. I'd be happy to win either of them."
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