Danilo Di Luca clung onto the leader's pink jersey in a killer climb Wednesday and is now odds-on to claim his first Giro d'Italia Sunday.
Di Luca came in fourth despite losing ground after a strong attack by veteran Gilberto Simoni on Europe's steepest cycling mountain here.
Battling back, Di Luca restricted the arrears to just 31 seconds.
Two-time winner Simoni, 36, is now just two minutes 28 seconds behind Di Luca in third place - but is unlikely to gain any more in the riders' last chance to shake up the standings, a time trial on Saturday.
Luxembourg youngster Andy Schleck lost just seven seconds to Simoni Wednesday and has a better chance to make up ground on Di Luca against the clock.
Schleck, 22, is now second overall at two minutes 24 seconds from Di Luca.
